With the advancement of implantable technology in the sensory world, new possibilities to improve the quality of human life have started to emerge. A wireless implantable body sensor network is a concept that has been studied for over a decade, where multiple different implantable sensors are integrated to create a network. The network relies on wireless links as the mean of communication between the sensor and actuator nodes through challenging medium of human tissues. In this paper, a microstrip antenna was designed to accommodate the constraints incurred by the human tissues environment and to provide a reliable transmission at 402 MHz frequency. A multi-layer human arm was used as the model and the simulation was run with High Frequency Structure Simulator (HFSS) software. Antenna parameters including return loss, gain, radiation pattern, and SAR values were obtained from the simulation as the reference value for future in vitro or in vivo experiments.