C-methyltransferase that methylates 8-demethylnovobiocic acid to produce novobiocic acid in the novobiocin biosynthesis pathway. Novobiocin is an aminocoumarin family antibiotic that targets bacterial DNA gyrases. 8-desmethylnovobiocic acid + S-adenosyl-L-methionine = H(+) + novobiocic acid + S-adenosyl-L-homocysteine Antibiotic biosynthesis; novobiocin biosynthesis. Belongs to the methyltransferase superfamily.