I am a foreign (single) student who entered US in 2004.
Currently, I am doing OPT after my graduation, so I have to maintain at least 20hrs/week.
I got W-2 form a few days ago, and realized they charged me Social security tax.
This is my very first income in US.
What I've heard is the employer is supposed to exempt it from my income.
Do I have to claim to my current employer or Do I ask IRS to return those amount?
This is my very first tax document. I don't know what to do.

And how long does it usually take to get it back?
My opt period expires in July, so I have to leave US till July. I don't even know I can receive my tax return.

Please answer me whoever has knowledge about tax for international student.

On F1/OPT you are exempt from residency for 5-years. You must file non-resident tax return Form 1040NR or 1040NR-EZ and Form 8843.

Your income is not subject to FICA taxes. If employer is withholding SS tax and Medicare tax, then tell them about your status so that they do no withhold these taxes. Send them email for refund of the taxes. If employer does not refund the FICA taxes, then you will file Form 843 with IRS. It is filed separately.

However, you must pay FICA taxes in 2009 as this is your 6th year. Read: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents (http://taxipay.blogspot.com/2008/03/us-tax-filing-requirements-for-non.html)