Repetitive work activities are often a cause of tendinitis, where the connective tissue surrounding the tendon becomes inflamed. If your job requires you to spend most of your time at a computer, at the very least make sure that you take frequent breaks. Get up, move around, and take every opportunity to complete other random tasks that don't involve keyboarding.
Proper ergonomics can also help. Make sure you have a proper chair with good back support, and don't let your elbows rest on the arms. You'll want to ensure your keyboard is placed at an appropriate height (most desks designed for writing are too high for keyboards -- the keyboard should be about the same height as your elbows). An ergonomic keyboard may also help. Finally, ensure that your posture is good, so that you're not bending forward to type.
Some people have had success with acupuncture, a good holistic option that can reduce pain and restore the ability to move problem-free. For supplementation recommendations and further reading, please consult our health notes: