TSH is only part of a puzzles, so without further information, it's very difficult to say. Under some circumstances, a TSH that low would mean a person has hyperthyroidism; under other circumstances, it could mean the person has a certain type of hypothyroidism. If the person is taking replacement thyroid hormones, it could mean the person is over medicated or everything is fine...
If you could please give us some more information, such as other tests that might have been ordered, along with their results and reference ranges, symptoms the patient has, etc., we'd be able to respond more fully.