A firmware update method and apparatus of a set-top box for a digital broadcast system is provided. A firmware update method of a set-top box for a digital broadcast system includes determining whether a newly received Code Version Table (CVT) following a public CVT which has been previously received and stored is the public CVT or a filtering CVT; and updating, when the newly received CVG is the filtering CVT, the firmware of the set-top box with a filtering firmware indicated by the filtering CVT.