Hi
Welcome to the MedHelp forum!
What you have is called mirror movement. Usually these disappear by ten years of age. If you do not have any other neurological signs, any tingling, numbness, memory problems, blackouts, etc then this could be a familial trait and other members in your family either in this generation or previous generations must have had it too.
The other possibility is that there is a brain infarct or localized demyelination etc in the brain and in such a case you could be having localized or generalized neurological symptoms.
Please consult a neurologist regarding this.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!
It is called mirror movements.
http://blogs.discovermagazine.com/notrocketscience/2010/04/29/a-single-genetic-fault-makes-one-hand-mirror-the-other/
Lynda