In this letter, we propose a simple algorithm to jointly estimate the symbol timing offset (STO) and carrier frequency offset (CFO) of wireless body area network (WBAN) signals. The preamble specified in IEEE 802.15.6 WBAN is used to achieve an accurate timing and frequency estimation based on the differential correlation. Simulations demonstrate that the proposed joint estimation scheme can be effectively employed to get accurate STO and CFO estimate with less complexity.