If you are trying to make a round disc to be a base for a pedestal (meaning a column that supports the table top), you've got a number of options.
3fingers already gave you one -- a jig that lets you move a router in a circle around the center point. These are available to buy or you can make your own very simply.
Do you have a band saw? If so, you can make a "circle cutting table" that clamps onto the table. All it really needs is a flat surface with a dowel peg 8" to the side of the band saw blade ... drill a hole in the piece you want to make circular, set the hole on the peg, away you go. A hole in the center of the circle shouldn't be an issue since you have to attach the pedestal column to the base somehow.
Or you can simply draw a circle on the board and cut it with a jig saw, saber saw, or even a hand saw, then sand it to the line.