There are certain types of mold and fungus that present with mushrooms. These are often found outside but are also found indoors, especially in areas where there's a high level of moisture or humidity. These mushrooms are potentially harmful and can spread to other areas when left untreated. The best way of removing the mold is by treating the area and removing the mushrooms.
Cover your hands with rubber gloves and pull the mushrooms off the wall or area, making sure to pull off both the cap and the stem. If you have problems getting the stem, try using a chisel to scrape it off the wall.
Place a dehumidifier in the area and let it run on high for at least 1 day, but preferably several days. The main reason behind the mold problem is the high levels of moisture in the area, and the dehumidifier reduces that moisture and dries out the area.
Apply a solution of antibacterial soap and water to the area with a dry scrub brush. Scrub the area briskly with the mixture, removing all traces of the mold and mold mushrooms. Rinse off the area with fresh water and let air dry.
Mix together an equal solution of hydrogen peroxide and water. Apply this solution directly to the affected area to kill off any traces of the mold left behind. This peroxide in the solution is affective at killing the mold and disinfecting the area.
Inspect the area for signs of any more serious damage. The mold can sometimes infect the area behind walls and get into the drywall. If this happens, you'll need to hire professional help. You should also look for signs that you've removed all traces of the mold and mushrooms.