A statement from the public prosecutor's office on Wednesday said the men were released due to a lack of evidence against them.
"We have interrogated all six. We have not found enough evidence to hold them therefore we have released them unconditionally," the statement read.
Interior Minister Shaikh Rashid bin Abd Allah al-Khalifa said this week the men were arrested to "prevent them committing dangerous operations which would have threatened people and possessions" in Bahrain, home to the US Navy Fifth Fleet.
Bahrain's neighbour is Saudi Arabia, which has been hit by a wave of bombings and shootings of foreigners allegedly carried out by Saudi-born dissident Usama bin Ladin's al-Qaida network.
Lawyers said the men were wrongly suspected of links to al-Qaida. "These are all pretexts. There are no justifiable charges against them. Nothing that would constitute a crime," lawyer
Abd Allah Hashim told reporters.
"I never felt any anxiety from the beginning because there were
no clear cut charges against us"
Farid Ghazi, a lawyer for Muhiddin Khan, said his client had been arrested because he kept antique daggers at home. "Knives in the kitchen are sharper than the daggers he had. This is ridiculous," Ghazi told reporters.
One of the six released men, Bassam Bukhuwa, said they should never have been held. "I never felt any anxiety from the beginning because there were no clear cut charges against us," he said.
Hashim said earlier the men, who were arrested early on Tuesday, were known to be Salafists and were rounded up because of their suspected ties to al-Qaida.
Salafist is a general term that Islamist movements in Sunni Islam use to describe their desire to return to what they say are the ways of early Muslims. In Saudi Arabia they are often referred to as Wahhabis.
A Salafist group fighting an Islamist uprising in Algeria is linked to al-Qaida.
Hashim said three of the detainees had been rounded up last year on suspicion of belonging to a cell believed to be linked to al-Qaida, but they had been released without charge.
He said one of them was detained last year in Saudi Arabia.
In February 2003, five Bahrainis were arrested and accused of planning "terror" attacks in the kingdom.
Tuesday's arrests had followed a warning by the US State Department on Friday about the possibility of attacks in the oil-rich Gulf region.