mableruth - fungus is needed to break down the mulch. There are thousands of different kinds of fungus. If there were no fungus, we would be over our heads with things that fungus breaks down into usable soil.
I'm guessing your fungus is doing the job Mother Nature intended it to do, so be glad it's there. Just don't eat it!
You might want to do a search for mycorrhizae. It's a beneficial fungus I purchase to add to my soil.