GO:0043333:   2-octaprenyl-6-methoxy-1,4-benzoquinone methylase activity
Catalysis of the reaction: 2-octaprenyl-6-methoxy-1,4-benzoquinone + S-adenosyl-L-methionine = 2-octaprenyl-3-methyl-6-methoxy-1,4-benzoquinone + S-adenosyl-L-homocysteine.