IEEE 802.15.4 (Zigbee) is the new standard that has been developed for low cost, low data rate and low power consumption wireless network. This paper provides a brief description of this standard including the Physical (PHY) and medium access control (MAC) layer. It focuses on developing MatLab/Simulink models for the Zigbee protocol and the performance evaluation of these models. Simulation has been run using MatLab and the results have been analyzed. The results show how the relationship between the signal Bit Error Rate (BER) and Signal to Noise Ratio (SNR) is affected when varying the data rate and the input signal power to the noise channel.