Most mushrooms growing in bonsai pots are either the fruiting bodies of beneficial fungus or imports from the bark commonly used in soil mixes, and most are completely harmless. The can be quite beautiful as well.
Thank you Mr. Heath. The pictures I included were the only ones I took and I can't blow them up enough to show any detail of the mushroom. Of course it's gone already. If any more come back I'll get a better photo. The article was great too. Thanks again.