Mediates C-terminal methylation of the isoprenylated C-terminal cysteine in A-factor mating pheromone and Ras proteins (PubMed:8289819, PubMed:11451995, PubMed:15611058). Does not have a preference for the farnesyl or geranylgeranyl moieties in the model substrates N-acetyl-S-farnesyl-L-cysteine (AFC) and N-acetyl-S-geranylgeranyl-L-cysteine (AGGC) in vitro (PubMed:15611058). [protein]-C-terminal S-[(2E,6E)-farnesyl]-L-cysteine + S-adenosyl-L-methionine = [protein]-C-terminal S-[(2E,6E)-farnesyl]-L-cysteine methyl ester + S-adenosyl-L-homocysteine Optimum pH is 7. Present with 2690 molecules/cell in log phase SD medium. Belongs to the class VI-like SAM-binding methyltransferase superfamily. Isoprenylcysteine carboxyl methyltransferase family.