Saplings

I have had a bonsai tree for a few months now and it is growing well. However the other day i noticed a little sapling starting to grow in the soil. My question is whether or not i can put it into another pot and grow it or just to leave it.

post a picture.
Is it a weed?

Yes, you can. It won't disturb the Bonsai (although it may kill the plant you're moving if you're not fast enough).
It may, as parker pointed out, be a weed, so please do post a picture.

Ed