The prosecution had charged the group with "forming an armed gang aimed at carrying out sabotage attacks".
The trial began in March with the 30 defendants in custody all pleading innocent to the charges.
Three of them had said they had been tortured and forced to sign confessions, Yemen's official news agency SABA reported.
Abu Bakr al-Rubaei, the leading suspect among those in custody, was among those who said he had come under duress to confess to the planned attacks.
He had allegedly admitted that he and others planned to carry out attacks against Western and US interests, as well as the homes of foreign diplomats in the country.
|The USS Cole naval destroyer was targeted |
by in 2000 [EPA]
He also told the court that he was asked by some groups to become involved in attacks in Yemen and Iraq, but that he refused involvement.
Al-Rubaei, who was sentenced to eight years' imprisonment, is the brother of Fawaz Yahya al-Rubaei, who was killed in a 2006 raid in Yemen's capital San'aa.
Fawaz had been convicted of an attack on a French oil tanker but later escaped from prison.
Al-Qaeda has an active presence in Yemen, despite government efforts to fight the terror network.
The Hadramout region of the country is the ancestral home of Osama bin Laden, al-Qaeda's leader.
Al-Qaeda was blamed for an attack on the USS Cole naval destroyer in the port of Aden, which killed 17 American sailors, and an attack on a French oil tanker that killed one person in 2002.
While Yemen offered its allegiance to US after the September 11, 2001 attacks, diplomats and outside experts have raised questions about the country's co-operation and inability to control its tribal areas.
Jamal al-Badawi was convicted in 2004 of plotting, preparing and helping carry out the Cole bombing.
He received a death sentence that was commuted to 15 years in prison.
A senior security official in Yemen said last month that al-Badawi was freed from jail after pledging loyalty to Ali Abdullah Saleh, Yemen’s president.
This month, the US said Yemeni officials had provided assurances that al-Badawi was still in prison.