For a broadband wireless access system, a method of configuring an IP address for a fixed/mobile station that changes from idle mode to receiving mode or when performing handover such that IP address configuration procedures are simplified. The base station determines whether the mobile station that changes from idle mode to receiving mode or performs handover needs to re-configure its IP address, and informs this to the mobile station, which can then selectively configure its IP address according to the needs of configuring its IP address.