Malik is Arabic, literal meaning "king." My guess is that it was used as a forename, and so as a surname derives from the given name of a male ancestor. It is found as a surname among Christians and Muslims. As a Muslim surname I suspect it is a shortened version of abd-al-malik, "servant of the King", i.e., God. I've heard of it as a surname in Lebanon (Christian), Iraq and Pakistan. It is also a surname among Bengali Hindus, but that name may have a different origin.