I am in OPT period for working?
Should I be charge the social security tax? Or how can I take it back from Company?
Thanks

Every one on F1/OPT is exempt from residency and FICA taxes for 5-years. Ask your employer to refund to the Social Security and Medicare taxes.
Read: Your U.S. Tax Return: Social Security and Medicare (FICA) Taxes for Non-resident Exempt Individual (http://taxipay.blogspot.com/2008/03/non-resident-exempt-individual-social.html)