If so you can try pull it out. Before doing so you should heat the area and apply oil. The heat will draw in the oil into the gaps. Then clamp the post into a vice or drill a hole through it and twist using a strong long screwdriver, trying to break it free. Once free, you can slowly jiggle it out.
Is there some seatpost protruding from the frame?
If so you can try pull it out. Before doing so you should heat the area and apply oil. The heat will draw in the oil into the gaps. Then clamp the post into a vice or drill a hole through it and twist using a strong long screwdriver, trying to break it free. Once free, you can slowly jiggle it out.