With the advancement made in low power BSN (Body Sensor Network) technology, wearable and portable biomedical devices are fast emerging as the next generation healthcare monitoring and/or medical diagnostic tools. For effective real time healthcare monitoring and/or telemedicine applications, the wearable or portable devices have to be equipped with transceiver electronics to facilitate data transfer between the medical devices and the user (e.g. doctors). One crucial design of such electronics is to have a robust and small communications system. It is well known that antenna array communication systems are capable of providing a high capacity in a mobile environment. However, the use of such systems for the biomedical applications described above leads to mutual coupling effect. This paper investigates the mutual coupling effect and its effect on system capacity. An expression to describe the effect of mutual coupling for channel capacity in wideband antenna array system is derived. Simulation result shows the impact of coupling effect on channel capacity in the wideband antenna array system.