Yes. Agree with Bro. slimey. There is water seeping into your wall. The paint discoloration and mold growth confirms that. You'll need to find out where the water seepage source is. Fix it, then repaint the wall.

It would help if you can give more information on the wall. Interior? Exterior? Location ? (bathroom, bedroom, etc) Do you know what is behind the wall (i.e. are there piping? ) The room behind the wall? (bathroom, toilet, outside garden)

Water is seeping from behind the wall. Source unknown. Could be the piping, could be water from shower from the bathroom, could be other source. You will have to find out. For the meantime awaiting repair you can wipe down the wall with a wet cloth. The mold comes off easily. Be warn ya, leaks do not go away by itself. You will have to fix it. Else it will grow into a monster problem (electricity trips, damaging foundation, etc). If that wall is on the first floor (i.e. not ground floor) it becomes even more crucial.