Catalysis of the reaction: S-adenosyl-L-methionine + histone H4 L-lysine (position 12) = S-adenosyl-L-homocysteine + histone H4 N6-methyl-L-lysine (position 12). This reaction is the addition of a methyl group to the lysine residue at position 12 of the histone H4 protein.
histone H4K12 methylation