The details of the thesis committee are specified in the University Catalog under the section "AP.6.9.3 Master’s Thesis":
The master's thesis committee is composed of at least three members of the graduate faculty, at least two of whom must be from the student's department or program. [Because all MAIS curricula are interdisciplinary, "student's department or program" is very broadly defined.] Faculty who are not members of the graduate faculty or other appropriate persons not affiliated with the university may serve as additional members. Committee members are appointed by the chair or director of the academic unit or program, or designee, after consultation with the student's adviser and the student.
The membership of the project committee is not specified in the University Catalog; it is determined by the Interdisciplinary Studies program.
Although the student is responsible for the development of the project committee, the master's project committee is appointed by the Interdisciplinary Studies director, who designates a member of the graduate faculty as the project committee chair. The committee is appointed after consulting with the student and adviser and consists of at least three people. The first member is the committee chair. The second member must be a member of the Mason faculty, graduate or otherwise. The third member may be a person with expertise on the project topic who holds at least a master's degree.
The University Catalog defines graduate faculty in section "AP.6 Graduate Policies" as follows:
The graduate faculty consists of all George Mason University tenured and tenure-track faculty. Other Mason faculty members, as well as individuals from outside the university, may be appointed to the graduate faculty by the Provost for a specified duration of time.
Students should not count on a non-graduate faculty member being made a member of the graduate faculty just to work with them. If you are not sure whether the person you are considering for your committee is on the graduate faculty, the best thing to do is to ask them.
While the catalog language governing committees suggests that the Interdisciplinary Studies director appoints a student's committee, this is merely an administrative measure. It is the student's responsibility to compose the committee in the first place, and it is never too soon to start thinking about it. There are a few of ways to research potential committee members:
For more ideas about the process of assembling the committee, consult the Student Handbook.