Does a RFID antenna need to be FCC certified?
A antenna by itself does not radiate, so can't be certified.  The entire unit of a intential radiator, including the antenna, absolutely needs to have FCC certification if you want to legally sell it in the United States.

If this antenna is connected to a receiver-only device that never intentionally radiates, then certification is not required.  However, it still must meet the radiation limits for a unintentional radiator, but it is up to you to make sure of that.  You don't have to get it tested, but if there is a complaint and the FCC finds it violating the limits, you're in deep doodoo.