"S-300, the air defense system, the contract has already been signed," Chemezov was quoted as saying at the Dubai Airshow.
A nuclear deal signed between Iran and world powers earlier this deal has put Sunni-ruled Gulf monarchies on edge: They fear Tehran's rapprochement with the West will allow it to pursue an expansionist agenda in the region.
Chemezov said Gulf countries had no reason to feel threatened by the deal.
"This is defense equipment. And we are ready to offer this defense equipment to any country," Chemezov later told Reuters in Dubai, speaking through interpreters.
"So if the Gulf countries are not going to attack Iran ... why should they be threatened? Because this is defense equipment."
He said that Saudi Arabia, arch-rival of Iran, had approached his firm "several times" requesting that it not deliver the equipment.
"Five years ago ... even now, up to now ... And we said that the S-300 is not capable to attack ... to reach the neighboring countries."
(Reporting by Alexander Winning in Moscow and Yara Bayoumy in Dubai; Writing by Maria Kiselyova/Yara Bayoumy, Editing by William Maclean)