This paper addresses the image-based visual servoing (IBVS) problem for a nonholonomic wheeled mobile robot with an active camera. We propose an IBVS scheme using a virtual barycenter of all feature points. The wheeled mobile robot is considered as a kind of nonholonomic mobile manipulator. De Luca, et al. have proposed an IBVS scheme for mobile manipulators based on the task priority method. However, De Luca's scheme dose not enough the original control objective in some cases. In this paper, we introduces the virtual barycentric point to perform IBVS for it in the primary task and IBVS for each real feature point in the secondary task.