Random number generators (RNG) are essential components for security system. RNGs are used in sensitive applications such as key generation and challenge-response based authentication. Therefore, ensuring the unpredictability of the generated bits is very important to keep the all system in safe. This paper presents RNG based on micro-scale bio-electrochemical cell system that provides alternative way of producing random bit streams. The system here is fabricated by using photolithography process and the main purpose of the micro device is analyzing the activity of microorganism that produces electrons to generate power. We use the randomly produced voltage value over time to generate strong random numbers which are successfully passed the NIST 800-22 statistical randomness tests after SHA-224 hash algorithm post-processing method. This alternative method ensures secure data transfer where bio-electrochemical cell system needs to be used such as environmental protection sensor networks, vehicles power by bio-electrochemical cell system, and portable electronic devices.