To guarantee seamless handoffs between access points (APs) is one of the most decisive factors in providing realtime applications such as voice over internet protocol (VoIP) in IEEE 802.11 networks. It is because in wireless local area networks (WLANs) there is no specific control channel for executing a handoff process and a mobile station (MS) has to search for new APs from channel to channel by temporarily disconnecting its association with the old AP. While previous studies are mainly focused on how to reduce the handoff latency, in this paper a channel scanning algorithm is proposed to schedule suitable time for performing a handoff process efficiently. In the proposed algorithm, the voice activity is taken into consideration, and the handoff process is performed during silent periods. Extensive simulations are conducted to investigate the performance of the proposed algorithm in terms of the handoff success probability and the packet loss rate, and the results obtained in this paper can serve as a good reference for the system design.