Until recently, the sonification of Virtual Environments had often been reduced to its simplest expression. Too often soundscapes and background music are predetermined, repetitive and somewhat predictable. Yet, there is room for more complex and interesting sonification schemes that can improve the sensation of presence in a Virtual Environment. In this paper we propose a system that automatically generates original background music in real-time called VR-RoBoser. As a test case we present the application of VR-RoBoser to a dynamic avatar that explores its environment. We show that the musical events are directly and continuously generated and influenced by the behavior of the avatar in three-dimensional virtual space, generating a context dependent sonification.