Mend has denied being involved in the attack
A court in Equatorial Guinea has sentenced seven Nigerians each to 12 years in prison for an attack on the presidential palace in February 2009.
They also received the equivalent of thousands of dollars in fines.
Several Equatorial Guineans accused of participating in the attack were released because of lack of evidence.
The government had said the attack involved Nigerian militants from the Movement for the Emancipation of the Niger Delta (Mend), which denied this.
The convicted Nigerians claimed they were on their way to Cameroon when their boat was driven off course by a storm and stopped by the Equatorial Guinea navy.
A group of attackers then tried to take the presidential palace in Malabo but were defeated in a gun battle by the army.
Equatorial Guinea is the third largest oil exporter in sub-Saharan Africa and has a history of coups, the last successful one being in 1979.
In 2009, British mercenary Simon Mann was given a pardon after being sentenced to 34 years in jail for his role in a 2004 coup plot.