Disclosed is a method for a terminal, which is in an idle state in a wireless access system that supports machine-to-machine (M2M) communication, updating an M2M group identifier (MGID), which identifies a multicast service flow that is shared by a group of M2M terminals inside an M2M group zone. The method can comprises the steps of: receiving from a first base station the MGID and the M2M group zone identifier of the first base station; receiving from a second base station an M2M group zone identifier of the second base station; requesting from the second base station an MGID update when the M2M group zone identifier of the second base station is different from the M2M group zone identifier of the first base station; and updating the MGID on the basis of a new MGID that is transmitted from the second base station as a response to the request.