Looks like a tiny saprophytic mushroom, which is common in moist, organic-rich soil. It’s too early to ID the exact type, but it’s not harmful to your plant. That said, it’s still a good idea to remove it. Mushrooms like this can be a sign that your soil is staying too wet or your humidity is running high. Gently pull it out, avoid disturbing the soil too much, and let the top layer dry a bit more between waterings. Improving airflow can also help keep them from coming back.