If you see mold on your soil, it is likely confined to the top layer. You can use a spoon to easily remove the mold. The visible mold in your soil is like a saprophyte, which is harmless to you and your family. However, leaving the mold there will leave your plant susceptible to root rot. If there is an extensive amount of moldif it has spread to the pot itselfrepot the plant. Use high-quality potting soil. Once the mold is scooped out, or your plant has been repotted, allow the soil to dry out before watering it again. If your plant requires moist soil, wait until the surface is dry. If not, you should wait until you have dry soil 2 or 3 inches down. Continue letting your soil dry like this in between watering. The mold spores are likely to be spread through the soil and it will easily come back if you don't do this. You can sprinkle cinnamon, baking soda, or apple cider vinegar on top of your soil as natural an anti-fungal. This acts as a natural deterrent to mold growth and won't harm your plant. Keep debris like rotting leaves and plant parts off of your soil. They can cause fungal growth. Trim your plants whenever necessary.

Summary:
Scoop away the mold. Let the soil dry. Add a natural anti-fungal to your soil. Keep the soil clean.