They are completely different but I can't really answer without a context. Mark usually means to correct something or to "Make a mark" on paper "The teacher marked my essay with a red pen". To remark is to make a statement or to say something. "You look pretty today", he remarked.

A "mark" can mean many things from a stain on a shirt, to a person's signature, to the victim of a elaborate con. A "remark" is a comment, or an observation. EX: Glancing at his watch, the young man remarked the time and remarked, "I'm late!"