This paper investigates a nonverbal interface system using bio-potential signals, such as EOG and EMG, measured by a simple brain-computer interface and discusses its possibility of controlling application in a hands-free manipulation system. A simple gesture recognition algorithm from EOG and EMG signals is presented to estimate the user's intentions and/or thoughts. To evaluate the effectiveness of the interface system, experiments of controlling a walkthrough application in 3D virtual space are carried out and the usefulness of the interface system is confirmed. As a practical application example, controlling an active camera with the interface system is also demonstrated.