"It is not ruled out that during the talks the Iranian side will raise the question about fulfilling a contract for the delivery of the S-300," the Interfax news agency earlier quoted a military source as saying.
The contract, which is reported to have been signed previously, is controversial as the weapons would significantly increase Iran's air defence capabilities.
Moscow has repeatedly denied it intends to sell Iran the S-300 systems.
Last October, Russia's foreign ministry said it had no intention of selling weapons to "troubled regions".
Anatoly Isaikin, head of the Russian Rosoboronexport, a state armaments monopoly, said it had not supplied the systems to Iran, but was able to do so if ordered by the government.
"If there is a decision from the president, a decision from the Russian government then Rosoboronexport will be obliged to fulfill it," Isaikin said in an interview with the Nezavisimaya Gazeta newspaper earlier this month.
The meeting between Najar and Anatoly comes amid mounting tension between Iran and the West, with fears that Iran is planning to build a nuclear bomb, a charge Tehran denies.