From IRS publication 519

Students and
Exchange Visitors

Generally, services performed by you as a nonresident alien temporarily in the United States as a nonimmigrant under subparagraph (F), (J), (M), or (Q) of section 101(a)(15) of the Immigration and Nationality Act are not covered under the social security program if the services are performed to carry out the purpose for which you were admitted to the United States. This means that there will be no withholding of social security or Medicare taxes from the pay you receive for these services. These types of services are very limited, and generally include only on-campus work, practical training, and economic hardship employment.

However, you are covered under the social security program for these services if you are considered a resident alien as discussed in chapter 1, even though your nonimmigrant classification (“F,” “J,” “M,” or “Q”) remains the same. Social security and Medicare taxes will be withheld from your pay.