Amnesty said the men, who were involved in anti-government protests last year and convicted by a military tribunal on charges that included "setting up terror groups to topple the regime," were prisoners of conscience who should be freed immediately.
All of them maintain their innocence.
The Court of Cassation in Manama is due to decide on Monday whether or not to grant the men's request to be released on bail, with a "small possibility" that their sentences will be quashed, Amnesty said.
"Monday's decision will be a real test for the Bahraini authorities and their allies, if they want to prove once and for all that they are genuinely committed to respecting and protecting human rights," said Hassiba Hadj Sahraoui, Amnesty's deputy director for the region.
"These men must be immediately and unconditionally released. Their sentences and convictions must be quashed," she added.
Sahraoui urged Bahrain's allies to put pressure on the authorities "to drop the pretence of reform and immediately back up their words with real actions."
In September, an appeals court upheld life sentences for seven of the activists, all Shiite, including leading figure Abdulhadi Khawaja, and jail terms ranging from five to 15 years for the others.
The defendants, who had played leading roles in month-long protests last year demanding democratic reforms, were being retried in a civil court after they were convicted by a special semi-military court of plotting to topple the Sunni ruling family.
Bahrain came under strong criticism from international human rights organisations over last year's crackdown on the Shiite-led protests.
An international panel commissioned by King Hamad to probe the government's clampdown found out that excessive force and torture had been used against protesters and detainees.