Muscle tension is uncomfortable and once you learn to recognize it you will see that most people hold tension in the shoulders and necks. Spending a lot of time at a desk or on a computer can cause tension here, as can stress or anxiety.
Stress and anxiety are stored in the body as tension. If you find yourself becoming anxious notice if you grind your teeth, causing tension in your jaw, or whether you hunch your shoulders or flex your stomach muscles. Practicing awareness like this can help to relieve muscle tension.
There are simple practices such as deep breathing or belly breathing, alternate nostril breathing and chanting “Om” which work so well in reducing stress. If you're finding that the tension is causing you muscle pain get a relaxing treatment. Try to get more sleep and find the root of your stress and anxiety problems.