Proper ergonomics improves productivity and reduces risks for injuries such as tendinosis, tension neck syndrome, and back injuries. Despite having ergonomics standards and guidelines for computer usage since the 1980s, injuries due to poor ergonomics remain widespread. We present ActiveErgo, the first active approach to improving ergonomics by combining sensing and actuation of motorized furniture. It provides automatic and personalized ergonomics of computer workspaces in accordance to the recommended ergonomics guidelines. Our prototype system uses a Microsoft Kinect sensor for skeletal sensing and monitoring to determine the ideal furniture positions for each user, then uses a combination of automatic adjustment and real-time feedback to adjust the computer monitor, desk, and chair positions. Results from our 12-person user study demonstrated that ActiveErgo significantly improves ergonomics compared to manual configuration in both speed and accuracy, and helps significantly more users to fully meet ergonomics guidelines.