The High Criminal Court jailed another defendant for five years on similar charges yesterday's hearing, BNA quoted prosecutor Nawaf al-Awadhi as saying in a statement.
Bahrain, home to the US Fifth Fleet, remains deeply divided three years after a quashed Shiite-led uprising, with persistent protests sparking clashes with police, scores of Shiites jailed on "terror" charges and reconciliation talks deadlocked.
The 12 defendants were charged with "possessing weapons, ammunition and explosives as well as manufacturing bombs for terror purposes," said Awadhi.
They planned to target members of the security forces and public figures to "spread chaos and terror" in the Sunni-ruled kingdom.
Also Read
According to the statement, some of the defendants had confessed to their involvement in the plot while others of the group remain at large.
The authorities last year increased the penalties for those convicted of violence, introducing the death penalty or life sentences in certain cases.
The International Federation for Human Rights says at least 89 people have been killed in Bahrain since the uprising began in February 2011.