This paper presents a compact and planar cavity-backed antenna for wireless body area network (WBAN) application at 5.8 GHz. The planar cavity is realized using Substrate Integrated Waveguide (SIW) technology. The SIW cavity consists of two rectangular-tilted slots and two metalized via holes. The slots are introduced on the top plane for radiation while metalized vias are introduced in the proximity of the slots to enlarge the impedance bandwidth. To evaluate on-body performance, a pork muscle equivalent phantom is used in simulation studies. The simulated -10 dB impedance bandwidth on-phantom is 270 MHz (5.62-5.89 GHz) which fully covers the Industrial, Scientific and medical (ISM) band. The SAR Value per 10 g mass of tissue is 1.48 mW/g with an input power of 100mW which is satisfactorily below than specified FCC limits. © 2019 European Association on Antennas and Propagation.