You can remove the mushroom if you want. The fungus will still remain in the soil, however there should be no danger in using the plants. All soil will contain fungi unless it has been sterilized.

Thanks so much!! I guess this is more common than I thought. I do appreciate it!

Not to worry...that's the very common "yellow potting soil mushroom ", Leucocoprinus birnbaumii. Peat-based potting mediums are often contaminated with the spores. Just pull it out before it matures.

I had a similar mushroom growing in one of my amaryllis, except mine was much fatter, and there were a LOT of them. When I unpotted the amaryllis, the soil was chock full of mycilium, and I had to bring out the 'big guns'-- wash the bulb clean and then sterilize with a fungicide. If your mushroom reappears you might want to get rid of that soil.

Happy gardening!

--Rick in CT