The Generic Access Network (GAN) developed by 3GPP extends services to unlicensed spectrum. A mobile station with multiple air interfaces can access 3GPP services through GAN and roam seamlessly between different radio access networks. However, resource management is a critical issue in GAN. To allocate GAN resources efficiently, we propose Adaptive Keep-alive Interval (AKI). By using AKI, an MS can send less signaling messages. In addition, AKI can increase system utilization by releasing unused resources. The proposed AKI is evaluated by extensive simulations. The results show that the proposed AKI can reduce signaling overhead and increase GAN utilization significantly.