My native language is not English, however I hold a Master’s Degree from an institution at which English is the language of instruction, do I still have to take the TOEFL exam?

Yes. Adequate command of spoken and written English is required for admission. Applicants whose native language is other than English and who do not hold the equivalent of a US Bachelor's degree from an institution at which English is the language of instruction are required to submit TOEFL scores.

See also: Graduate