In this paper, and for the purpose of optimizing the performance of WiMAX mesh networks using multiple channels, we search the minimum number of channels that maximizes the throughput capacity. WiMAX operates in the licensed bands, so it is important to use only the sufficent number of the scarce wireless channels. Moreover, it helps to decide whether or not to use frequency spatial reuse (FSR) that incurs additional control information, which is relatively large as an accurate knowledge of the interference state at each SS must be accumulated at a central entity that sets the schedule (which is the BS in our case). Numerical simulations show that in most of the cases, with 3 or 4 channels, the maximum throughput capacity can be obtained for single interface WiMAX mesh networks, and no gains are obtained if more channels are used.