F-1 student regulations permit you to be enrolled in fewer than 3 course credits during your final semester. However, the credits you take during that final term must be “required” for you to receive your degree. The course can be a general ed requirement, a required elective or a required course in your major. It can also be your thesis course IF the thesis in your major requires classroom attendance – series of lectures for instance. The class or classes you take must require classroom attendance during that final semester. In other words, it cannot be just your thesis (requiring only independent research) that you have left to finish. Therefore, you need to plan your program accordingly.
This is the guidance provided by the Student and Exchange Visitor Program (SEVP):
"If a student needs only one course to finish his or her program of study, it cannot be taken through online/distance education. There must be a physical presence requirement for the course. If a student remains in the United States without reporting to any class, it becomes a security issue and cannot be allowed."
Share this information with your Academic Advisor so there is no misunderstanding as you come to the end of your studies. See International Student: Completing Your Program in 7 Semesters for further elaboration on possible end of program choices.
To obtain SEVIS authorization to enroll below full time in your last semester please complete the RCL Request Form for Academic Reasons [pdf], and submit it to your international student advisor prior to dropping below full time.