A system and method for updating a sleep identifier (SLPID) of a mobile station (MS) in a broadband wireless access (BWA) communication system having a sleep mode in which there is no transmission data and an awake mode in which there is transmission data. Upon recognizing a need to update an SLPID allocated to an MS in the sleep mode in the initial phase of the sleep mode, a base station (BS) reallocates a new SLPID to be allocated to the MS and transmits SLPID update information to the MS. Upon receiving the SLPID update information for its current SLPID during the sleep mode, the MS updates its current SLPID with the reallocated SLPID according to the received update information.