The George Mason University 2009 - 2010 University Catalog states:
Absences from final exams will not be excused except for sickness on the day of the exam or other cause approved by the student’s academic dean or director. The effect of an unexcused absence from an undergraduate final exam shall be determined by the weighted value of the exam as stated in the course syllabus provided by the instructor. If absence from a graduate final exam is unexcused, the grade for the course is entered as F.
(http://catalog.gmu.edu/content.php?catoid=5&navoid=104#final_exams)
For information on being absent with permission from a final exam, see the Additional Grade Notations section in the University Catalog.