Methyltransferase involved in methanogenesis in the methanol pathway. Catalyzes the methylation of the MtaC-bound cob(I)amide. Co(I)-[methanol-specific corrinoid protein] + H(+) + methanol = H2O + methyl-Co(III)-[methanol-specific corrinoid protein] Heterotetramer, composed of 2 MtaB and 2 MtaC subunits. Belongs to the MtaB family.