They denied the charges of "preparing and executing attacks against another country, as well as training to use arms, being members of a banned organisation, and financing terror attacks," Hashem said.
"Our defence is based on the absence of proof," he said, adding that the trial has been adjourned until November 20.
Hashem had told AFP on October 7 that four defendants were facing charges.
The three defendants in court are members of a group of six arrested in August on suspicion of belonging to an Al-Qaeda inspired cell. The other three were released last week, their lawyer Farid Ghazi said.
Local media reported on August 9 that police had arrested three people accused of belonging to a cell plotting attacks on US targets in Bahrain.
The small Gulf archipelago is home to the US Navy’s Fifth Fleet and has been designated by Washington as a major non-NATO ally.
The Bahraini government has introduced tough new anti-terror laws despite strong opposition from local rights groups.
