There are simple and complex explanations for this shaking. Sometimes the explanation is simple and treatable. Sometimes the situation is complex with further complications on the way. You need a good work-up from an M.D., including acetacholinesterase levels. Sometimes this is due to simple calcium deficiency, treatable by taking a glass or two of milk.
You dont say when ,is it all the time or when you are at rest or doing an activity, see your Doctor if it persists and for no reason.