Catalysis of the reaction: S-adenosyl-L-methionine + tRNA containing N6-threonylcarbamoyladenosine at position 37 = S-adenosyl-L-homocysteine + tRNA containing N6-methylthreonylcarbamoyladenosine at position 37.
Comment:
This activity is distinct from tRNA (adenine(37)-C2-)-methyltransferase activity (GO:0002935) in that it requires the presence of a threonylcarbamoyl modification.