Assistive systems provide tools to increase workers' productivity for industrial assembly and maintenance tasks. Current research focusses on showing step-by-step instructions in the user's field-of-view using projections or smart glasses. In this paper we present our concept for an assistive system for assembly tasks, which makes use of augmented reality technologies in combination with sensor-based systems to provide context-sensitive feedback. By this means we create an assistive environment that provides information at the right time and furthermore checks the correctness of tasks performed. Our goal is to provide a sensor-based workstation for assembly and maintenance workers that speeds up work and reduces error rates.