This work demonstrates the impact of human body on an 800 MHz inset fed rectangular microstrip patch antenna characteristics. The antenna was simulated over a human phantom model consisting human thigh muscle using CST Microwave Studio. The distance between the antenna and human thigh muscle was varied to analyze the changes in antenna performance for waveguide port feeding. The results exhibited significant changes in antenna characteristics, especially the shifting of center frequency to a lower value due to the human body. Specific Absorption Rate (SAR) was studied as well to illustrate how on-body communication or mobile phone antennas of GSM band might affect human body when mobile phones are kept in pants pocket.