For saving battery energy of mobile station (MS) and scarce radio resource, the idle mode operation is a significant portion in IEEE 802.16e Mobile Wireless Metropolitan Area Networks (WMAN) system. Current IEEE 802.16e standard specifies the management mechanism of idle mode and the paging procedure at physical (PHY) layer and medium access control (MAC) layer in order to increase life time of a MS. In this paper we analyze and model the idle mode operation in the IEEE 802.16e WMAN system; and two major performance characters in the idle mode operation, average power consumption and average frame response delay, are evaluated based on the proposed mathematical analysis. This work, in fact, is a first-moment mathematical model for the performance analysis of idle mode operation in IEEE 802.16e WMAN system. We expect that these performance models presented by mathematical formulas can be used in initial system planning and evaluation of idle mode design, before progressing the idle mode system simulation and system implementation.