A network robot system integrated with various types of robots via ubiquitous networks is a new concept which introduces an interactive robot living together with people. In this paper, we present a tangible network robot system composed of a mobile robot and vision sensors embedded in an environment, and show human behavior recognition methods necessary for providing diverse services desired by the people in good time. Typical human behaviors are described with logical sensors which are defined through data fusion processes spatially and temporally with the physical sensors of the mobile robot and those in the environment. Our system can be utilized to make human-robot communication and interaction friendlier and smarter