Catalyzes the post-translational methylation of isoprenylated C-terminal cysteine residues. [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 Competitively inhibited by N-acetyl-S-trans,trans-farnesyl-l-cysteine (AFC). Ubiquitously expressed. Expressed at higher levels in the cerebellum and putamen than in other brain regions. Abundant expression seen in the Purkinje cells and pontine neurons. Belongs to the class VI-like SAM-binding methyltransferase superfamily. Isoprenylcysteine carboxyl methyltransferase family.