Mold on houseplants can represent many things. You could be creating a habitat more conducive to mold growth than houseplant growth. You could have gotten a batch of soil full of mold spores, or you could be watering too often. Whatever the case, mold is not necessarily something that will kill your houseplant and with a little persistence, it's easy enough to get rid of.
Stop overwatering. Too much water creates perfect conditions for mold to grow on soil. Water, then wait until the first 2 to 3 inches of soil are almost all the way dry before you water again. Many plant do not need daily watering. Monitor your soil to see if less frequent watering gets rid of your mold problem.
Add a fan to the area where you keep your plants. The increased air circulation will decrease the humidity surrounding the container and will help that top layer of soil dry out better.
Mix a solution of half water, half white vinegar in a spray bottle and mist the surface of your plant's soil. This will increase your plant's soil pH, making it more acidic and less hospitable to mold.
Add a few drops of dishwashing liquid to a bowl of warm water. Dab a sponge or paper towel into the water and use it to clean off any mold that appears on the surfaces of your plants. Mist the plant with the vinegar solution to retard future mold growth.
Allow the top 2 inches of your soil to dry out, then use a spoon or small garden shovel or hand spade to carefully remove the top layer of soil. Replace it with pasteurized soil made specifically for houseplants.