No, it wasn't. 9/11 was an Arab deal, hence the Arabs who done did it.
In fact, just months before, Iran was gearing for war with the Taliban because of a meeting where they killed a bunch of Iranian diplomats and journalists.
Secretly the Clinton Adminstration implored Iran not to do so. They didn't.
Ironically, if they did, 9/11 wouldn't have happened, and Iran would have been labeled terrorist for attacking the Taliban who would have utilized bin Laden's Al Queda as well.
FUN FACT: The intel Iran gathered in planning that excursion was utilized by the US for its invasion of Afganistan. Without it the war would have been delayed some months. Then Bush thanks them by calling them part of the Axis of Evil.
Figures, huh?