The answer is, of course not. There was no doctrine of Purgatory in Cyprian's day, and consequently no doctrine of indulgences either. But occasionally Cyprian's Epistle XIII is trotted out as evidence of indulgences in the 3rd century (example).
A typical presentation of Cyprian's words is presented thus:
"Those who have received a libellus from the martyrs and with their help can, before the Lord, get relief in their sins, let such, if they be ill and in danger, after confession and the imposition of your hands, depart unto the Lord with the peace promised them by the martyrs " (Ep. xiii, P.L., IV, 261).
What's usually not mentioned is that this "libellus" is a certifiate: a piece of paper filled out by the martyr. In Epistle XII, Cyprian refers to these certificates as "by their letters to us." It's not 100% clear which martyrs Cyprian has in mind (at least not from this particular epistle). In Epistle VIII, Cyprian writes to certain martyrs, to wit men about to die for their faith.
In Epistle IX, Cyprian conveys the fact that apparently the martyrs had written to him requesting that those who had lapsed during the time of persecution be restored to communion when the time of persecution was over. He explains that some were willing to accept people back on the bare word of the martyrs, before the persecution was past, before there was repentance, and even before the martyrs themselves had been martyred! Cyprian explains that this is not proper. Furthermore, Cyprian explains that "even if the martyrs, in the heat of their glory, were to consider less carefully the Scriptures, and to desire anything more, they should be admonished by the presbyters' and deacons' suggestions, as was always done in time past."
From Epistle X, we gather that the martyrs had identified "certain of the lapsed" for this benefit. In Epistle X, though, Cyprian has to politely decline their request in part, for he insists that there must be repentance of sin before their can be a granting again of communion. Furthermore, toward the end of the epistle (part 4), Cyprian urges the martyrs to be specific in their commendations. Cyprian explains that they should name names, and only designate those "whose penitence [repentance] you see to be very near to full satisfaction."
In Epistle XI, Cyprian explains that "no one can come to communion unless the hands of the bishop and clergy be first imposed upon him" and therefore urges "how much more ought caution and moderation, according to the discipline of the Lord, in these gravest and extremest sins!"
For you see, the problem is this: in the time of persecution, many abandoned the faith. It was an enormous task for the elders (even assisted by the deacons) to examine those who wished to return to communion. The testimony of the martyrs was viewed as compelling - partly because the martyrs could themselves be trusted (for they were willing to die for their faith) and also an honor for the martyrs as indicated in part 3 of Cyprian's Epistle XIV.
In short, in the historical context, when Cyprian writes: "Those who have received a libellus from the martyrs and with their help can, before the Lord, get relief in their sins, let such, if they be ill and in danger, after confession and the imposition of your hands, depart unto the Lord with the peace promised them by the martyrs," we understand that Cyprian is referring to restoration into the visible church of Christ: a restoration of fellowship and communion, and of peace with the church.
Even so, Cyprian immediately goes on to contrast them with the "others who, without having received any certificate from the martyrs, are envious ..., must wait, in dependence on the protection of the Lord, for the public peace of the Church itself."
What is Cyprian trying to convey? He's explaining that even though it is not technically proper to begin restoring the lapsed while the church is being persecuted, those who appear to be at death's door may be received back, assuming the other conditions for re-acceptance are met.
In Epistle XIV, Cyprian explains that he "wrote twice" and indicated that those qualifying in dire straits should be "remitted to the Lord." In the same epistle he goes on to explain how he came to provide epistles XII and XIII, namely because there way too many, and way too many spurious, certificates being written - and lapsed were being welcomed back in, who should have been excluded. But after this had been stopped, those who had certificates started to stir up trouble, basically demanding that the churches honor their certificates. So, the purpose of XII and XIII were to limit the acceptance of the certificates to those at death's door, at least until the persecution was over.
In short, even with the certificates of the martyrs, Cyprian goes in Epistle XXVI to state that "although they [i.e. certain lapsed folk] had received certificates from the martyrs, nevertheless, that their satisfaction might be admitted by the Lord, these persons beseeching have written to me that they acknowledge their sin, and are truly repentant, and do not hurry rashly or importunately to obtain peace ...."
From all this context, we see that these certificates of the Martyrs were, in essence, personal commendations to the effect, "I know this person - he is truly sorry for his sins, please accept him back into the church of God." This was taken by some of the certificate recipients to their spiritual benefit - but by others to a demanding and insistency, as though the certificates were "Get out of Excommunication Free" cards.
So we even read a response from the presbyters and deacons of Rome to Cyprian, in which they explain "Let them, then, see what they are trying to do in this matter. For if they say that the Gospel has established one decree, but the martyrs have established another; then they, setting the martyrs at variance with the Gospel, will be in danger on both sides. For, on the one hand, the majesty of the Gospel will already appear shattered and cast down, if can be overcome by the novelty of another decree; and, on the other, the glorious crown of confession will be taken from the heads of the martyrs, if they be not found to have attained it by observation of that Gospel whence they should become martrys; so that, reasonably, no one should be more careful to determine nothing contrary to the Gospel, than he who strives to receive the name of martyr from the Gospel." (Ep. XXIX, pt. 2)
Notice how both Cyprian and the Roman presbyters agreed that even if the martyrs thought otherwise, it was their loss: not the Gospel (word from the Romans) /Scriptures (word from Cyprian). But finally, one could turn to the end of the second epistle from the roman presbyters to Cyprian, in which they assent to his thought of making an exception for those on death's door. For they essentially repeat his ideas and expound and (most notably, slightly expand):
"but of such as impending death does not suffer to bear the delay, having repented and professed a detestation of their deeds with frequency ; if with tears, if with groans, if with weeping they have betrayed the signs of a grieving and truly penitent spirit, when there remains, as far as man can tell, no hope of living; to them, finally, such cautious and careful help should be ministered, God Himself knowing what He will do with such, and in what way He will examine the balance of His judgment; while we, however, take anxious care that neither ungodly men should praise our smooth facility, nor truly penitent men accuse our severity as cruel."
After such an investigation, I think we can conclude that neither Cyprian or his colleagues in Rome had any concept of Indulgences in mind in the various letters they exchanged. They were concerned, very concerned, about proper church discipline, and had very serious reservations about those who had lapsed during time of persecution.