To minimize the power consumption of a mobile device, mobile WiMAX based on IEEE 802.16/802.16e defines three power saving classes for transmitting different types of data traffic. However, the standard specification does not suggest a power saving class for transmitting background TCP traffic, such as a long FTP session. This paper investigates the energy efficiency of TCP transmission over a WiMAX network under different MAC configurations, wireless and wired traffic conditions. We conduct a number of experiments in a real WiMAX test-bed and obtain power consumption parameters of a WiMAX network interface card (NIC). These parameters are further fed into the network simulator 2 (NS-2) to evaluate the energy consumption of TCP transmission in a large-scale WiMAX network. Experimental and simulation results demonstrate that the IEEE 802.16 bandwidth request mechanism introduces considerable power consumption overhead in TCP transmission. Moreover, the energy consumption of a long TCP transmission session in a WiMAX network can be significantly reduced by applying the power saving class type II and base station-proxy mechanism.