Student activist Vahid Abedini said that several hundred students protested outside as Ahmadinejad was delivering the speech to selected guests in a hall inside the university.
Abedini said that although Ahmadinejad responded to students' questions during his visit to Columbia University in New York last month, "he's not ready to listen to the questions of students at Tehran University and answer them."
Students had listed 20 questions they wanted to ask Ahmadinejad on human-rights issues -- including the expulsion of students from classes because of their political activities -- and Iran's foreign policy, including Ahmadinejad's statements questioning the extent of the Holocaust.
Before and during the president's speech, activists chanted "Death to the dictator!" and other anti-Ahmadinejad slogans.
Liberal-minded students accuse Ahmadinejad of clamping down on dissent on university campuses. In December, a speech by Ahmadinejad at another university in Tehran was disrupted by students hurling firecrackers and burning his picture.
Several students have also been expelled from school or have been blacklisted on official documents if they participated in student activities deemed by officials to be antigovernment.
(with material from agency reports)