I found these definitions:
Probably Jamaican, in which case it comes from the TV game shows, Master of Ceremonies (although the term existed before TV). It was the only person at a gathering that was allowed to use the microphone. Could also stand for Microphone Controller, Mic Checka. The term, MC, stand for Master of Ceremonies --- A Tribe Called Quest (Midnight Marauders [1993]).
MC, (or Emcee) a skilled rapper. True MCs use skills that are often ingnored in hip hop today. These skills include wordplay / punchlines, metaphors, similies, multis, flow and switch ups.