GO:0004671:   protein C-terminal S-isoprenylcysteine carboxyl O-methyltransferase activity
Catalysis of the reaction: S-adenosyl-L-methionine + protein C-terminal S-farnesyl-L-cysteine = S-adenosyl-L-homocysteine + protein C-terminal S-farnesyl-L-cysteine methyl ester.