If this is a sealed terr, there isn't much you can do other than learn to live with it. Mold naturally wants to grow in humid environments. It might go away once it has decomposed what it's 'eating'. If this is an open terr, you could try adding a fan for increased air circulation, or try spraying a baking soda solution on the surface of the soil. I don't know a specific recipe, but you might be able to find one on the houseplants forum. Or try covering all of the soil with a decorative mulch like small rocks, sand, bark chips, or even moss.