A military court in Manama sentenced the dissidents to terms ranging from one to four years for "participating in illegal demonstrations and inciting hatred against the regime" during mass protests, the human rights group said.
Fadhila Mubarak Ahmad, the first woman to be convicted in the unrest, got four years.
"These eight activists appear to have been sentenced to jail terms for doing no more than exercising their legitimate right to demonstrate," said Malcolm Smart, Amnesty's director for the Middle East and North Africa.
The defendants were held without arrest warrants, were denied family visits and had very limited access to lawyers, Amnesty International said.
Human rights activist Abdulhadi al-Khawaja told a military court in another trial police threatened him with rape while holding him in secret detention. He was immediately hustled out of the courtroom.
Al-Khawaja is among 21 opposition members on trial for leading the demonstrations in February and March. Seven of them are being tried in absentia.
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