In ubiquitous networking environments, we generally need two or more heterogeneous communication systems coexisting in a single place. Especially, wireless local area networks (WLANs) based on IEEE 802.11 specifications and wireless personal area networks (WPANs) based on IEEE 802.15.4b or g specifications need to coexist in the same Industrial, Science and Medial (ISM) band. If the WPAN communication coverage is expanded using a cluster-tree network topology, then the 802.15.4 network is more susceptible to interference from neighboring WLANs. In this paper, we propose an adaptive interference-aware clustering algorithm using multiple channels in a WPAN in the presence of WLAN interference. The algorithm includes interference detection and avoidance schemes to adaptively reconfigure multiple channels in an IEEE 802.15.4 cluster-tree network to avoid interference from WLANs. To evaluate the performance of the proposed algorithm, the frame error rate (FER) is measured in a real network testbed. The measurement result shows that the proposed algorithm is effective in an IEEE 802.15.4 cluster-tree network in the presence of multiple IEEE 802.11 interferers.