to expand on the last response, if you type with your right hand as the dominant, that might be keeping your right hand warm, try using your left hand more.  I type more left hand dominant and I get the reverse of your problem.  My left hand is warm and my right is cold

Do you use a computer at work? This could be caused by sitting at the wrong height for long periods of time. 

there is a problem with the blood supply of the hand,it might be dangerous also. it usually happens with the people who are smokers to say regular and heavy smokers. if it is so than quit smoking.