Yes there is - at least there was on mine. It a soft foam gasket - not wax like a traditional toilet. Mine wasn't in too bad of shape, but it can become crushed in spots and potentially leak (if not fluids, odors from the holding tank).
I replaced mine this spring as part of maintenance. The part was around $5. Very easy to do. Drain the tank, disconnect the water supply from the stool, disconnect the two bolts on the floor flange, lift toilet and remove ( I put down a plastic bag in the shower pan to set it on), remove old gasket, install new gasket, and install in reverse order.