You will usually get condensation if you have warm air (like air lacking circulation) settling on a cold surface (an outside wall) the only real cure is to move anything away from the said wall a little to allow air movement, lowering the temperature of the room will also help!!
condensation = warm air holds a lot more moisture than cold air, so when this warm air comes into contact with a cold surface, a window is a perfect example, it will release this moisture against that surface.
now if that surface stays moist through lack of circulation, mould could grow, you may be able to kill the mould but you still have the problem of trapped moisture which will eventually damage the decoration, wall paper etc and then the plaster on the walls!!
You need to look at the cause and deal with that!!!