Objection 1: It would seem that there is no distinction between actual grace and karma. For both are external causes of a person's future behavior. Therefore there is no distinction between them.
Objection 2: Furthermore, karma and actual graces both influence the state of an individual after death. For karma, we are told, can influence how an individual is reborn; and grace certainly influences their judgment to heaven or hell. Therefore, etc.
Objection 3: Furthermore, like actual grace, karma affects an individual based on their previous behavior. Therefore, etc.
On the other hand, karma appears to be automatic and objective, a particular understanding of how one's behavior influences one's future state. Not only do good actions produce good results, but bad actions produce bad. But although good actions will result in further actual graces, there is no statement that bad actions will result not only in a deprivation of grace by God in this life, but even of a specific obstacle to grace. Therefore there is a difference between actual grace and karma.
I answer that there is a distinction to be made between actual grace and karma, in a number of ways. In the first place, grace is a gift granted to one by God:
Grace is favor, the free and undeserved help that God gives us to respond to his call to become children of God, adoptive sons, partakers of the divine nature and of eternal life.
(Catechism of the Catholic Church, paragraph 1996; bold emphasis added)
But karma does not require to be granted by any being; it appears to be part of the structure of the universe:
a man of good acts will become good, a man of bad acts, bad;
he becomes pure by pure deeds, bad by bad deeds
(Brihadaranyaka Upanishad 4.4.5)
Furthermore, grace is granted to humans so that they may grow to become more like God (that they may advance in the process of theosis; see the quote above from the Catechism). Karma, on the other hand, does not appear to have any particular purpose.
For at least these two reasons, it appears that one must draw a distinction between actual grace and karma.
Reply to Objection 1: As discussed above, karma is not granted to one person by God, but grace is.
Reply to Objection 2: Although karma controls the state in which one will be reborn after death, grace does not in itself control whether one will be saved after death. Rather, the will of God, judging us as to our faith and works, accomplishes this.
Reply to Objection 3: As discussed above, karma can appear in both negative and positive forms, while grace is a purely positive gift of God.