How to get rid of mold on drywall
Wiping the the mold with some water-diluted bleach should eliminate the mold.  For good measure consider applying a mildew-resistant primer like "Kilz".

You will want to ensure the source of the moisture causing the problem has been fixed as well as check for mold behind the baseboard.  If you want to be extra thorough, cut out a small piece of the drywall and make sure there is not mold behind the wall surface you can see.