This paper proposes a motion control algorithm for an active type of robotic mobility aid based on passive behavior concept. Passive behavior is an important characteristic of a system that provides mobility to elderly or person with walking disability. It allows the user to control the system based on intention. Passive behavior is implemented using imposed desired dynamics, which represents the actual behavior of passive system. This approach uses user intention represented by applied force/torque to derive the mobility aid desired motion. In addition, a guideline in parameter selection of the desired dynamics is also presented. This guideline is used to ensure the stability of the active robotic mobility aid with passive behavior. Experimental results are presented to show the validity of the proposed control method.