is it bad if there is a mushroom growing in my house plant?

It doesn’t make any difference. You probably got some mushroom compost in your
planting mixture with some mycelium still in it. Does it look like a nice little white button mushroom? That would support my theory. But I wouldn’t eat it.
The reason it doesn’t make any difference is that mushrooms and green plants are different species with different needs, and don’t compete. See Michael Pollan’s The Omnivore’s Dilemma for much more interesting facts on this topic.

thanks!—that’s a great answer. I bought the plant 4 years ago and haven’t put any compost in since then, which is why I was surprised to see the mushroom.Don’t worry-not planning on eating it! But thanks for letting me know that it’s harmless to the plant.