The need for Wireless Body Area Network (WBAN) technology has been increased rapidly. It has been adopted in many applications such as medical and military. Due to the nature of WBAN environment and transmitted data (sending data over unsecure wireless network and the sensitivity of data), there are several security challenges in WBAN, which restrict WBAN utilization. One of the security challenges in WBAN is replay attack.Also the WBAN adopted Advanced Encryption Standard (AES) in CCM (Counter with CBC-MAC) mode for the message confidentiality and message authenticity. However, brute force attack can break AES secret key in a reasonable time within high speednew technologycomputers.This paper suggested a security protocol to improve the WBAN robustness against replay attack by using Multiple Key-Protocol-Advanced Encryption Standard to show its improvement for key strength against secret key breaking.The mathematical calculations proved that the suggested multiple key protocol increases the secret key strength and security system complexity.