Is there anything unusual about your job or your paychecks? A person could be exempt from income tax (box 1 wages = zero) but still pay social security and medicare tax if all their income was put into pre-tax benefits like health insurance premiums, pre-tax retirement account, flexible spending account, health savings account. There may be some cases where employees of international organizations like the U.N. or certain corporations might be exempt from income tax but still subject to social security. Or, it could be a mistake by your employer.
