The court gave the defendants sentences ranging from four to 10 years. It was not immediately clear how many would serve the maximum sentence.
The court ordered the release of six others who had already spent about 18 months in detention. They were found guilty of supporting al-Qaida but not direct involvement in attacks. They will be under government monitoring after their release.
Journalists were in the courtroom.
Yemeni President Abed Rabbo Mansour Hadi has ordered trials for dozens of al-Qaida suspects held without charges for over a year.