Nonresident aliens who are students, teachers, or trainees, and are temporarily present in the U.S. under an F, J, M, or Qvisa, must file a return only if they have income that is subject to withholding, even if no tax was withheld. (Caution: Even if they are exempt from filing a return, they must still file a tax form. ) But even students and scholars who are not required to file returns should do so if they are eligible for refunds.