The New York-based human rights watchdog highlights the cases of Rafael Matos Montes de Oca, Emilio Planas Robert and brothers Alexeis, Diango and Vianco Vargas Martin.
Javier Zuniga is special adviser for Amnesty. He says in a statement that their detentions are "only the tip of the iceberg for Cuba's repression of free speech."
Cuban officials deny holding any political prisoners. The government and its supporters call dissidents "mercenaries" who take foreign money to try to undermine the island's Communist system.
In recent years Cuba has cleared its prisons of internationally recognized prisoners of conscience. Activists say authorities have turned to brief detentions instead.