The suspects were arrested by Azerbaijani authorities in March and accused of having links to Iran's Revolutionary Guards.
Azerbaijan's Interior Ministry announced in March that AK-47 assault rifles, guns, and explosives were confiscated from the suspects.
The trial is being held behind closed doors.
Relations between Tehran and Baku have soured since it was reported in February that Azerbaijan had purchased some $1.6 billion of weapons from Israel.
Also in February, Iran accused Azerbaijan of allowing Israeli spies to use Azerbaijani territory, while Azerbaijan arrested an unspecified number of people, saying they were linked to Iran and were planning attacks in Azerbaijan.