The official Bahrain News Agency confirmed six arrests, but said only that they were made "to prevent them from committing dangerous acts that threaten property and people."
Quoting Interior Minister Shaikh Rashid bin Abd Allah al-Khalifa, the agency said the arrests followed in-depth investigations and that the cases would be referred for prosecution.
Some of those targeted had been under suspicion elsewhere in the Gulf, and relatives say computers, compact discs - including children's games and educational CDs - and audiotapes were seized from some of their homes.
The raids were carried out around 1am on Tuesday (2200 GMT Monday), when the men were taken from their homes, Abd Allah Hashim, a lawyer representing five of the detainees said.
"My clients were picked up early this morning, and I believe they have no links to al-Qaida," Hashim said. He said he had spoken with three of his clients by telephone.
Interior Ministry officials did not answer telephone calls and the Information Ministry said it had no immediate comment.
Brothers Yasir, 27, who owns a used car dealership, and Umar Abd Allah Muhammad Kamal, 18, were among those arrested in separate raids in east Riffa, an upscale, largely Sunni Muslim neighbourhood.
"As soon as my husband answered the door, they just barged in," said Yasir Kamal's wife, Umm Saad.
"I kept asking them what they were looking for and what we had done. They just wouldn't say anything at all. After the search was over, they took my husband away," Umm Saad said.
Yasir Kamal's computer, CDs and audiotapes were seized, she said. Umm Saad said her husband had been detained in Kuwait last year and eventually deported home to Bahrain. She said he was not told why.
The home of the two men's brother-in-law, locally known Muslim healer Shaikh Muhammad Salih, was also searched.
Bahrain is considered less
conservative than other Arab states
Salih recently spent nine months in Saudi jails being questioned about ties to "militants", relatives said. He was not detained on Tuesday, but his father-in-law, Abd Allah Muhammad Kamal, said he was placed under house arrest.
The four others detained were identified by Hashim, the attorney, as Bassam Bukhuwa, Bassam al-Ali, Muhiddin Khan and Ali Khan. It was not immediately clear whether the Khans were related.
Bukhuwa, al-Ali and Muhiddin Khan had been detained in February 2003 in a weapons case, but later were released. In that case, police seized guns and ammunition from five people allegedly planning attacks in Bahrain.
Only one of them ultimately was charged, tried and convicted, receiving five years in jail for illegal possession of weapons.
Bahrain, closely allied with the United States, is home to the US Navy's 5th Fleet. The tiny island is far more relaxed and Westernised than Saudi Arabia, which is just a short drive away across a causeway over the Gulf.
"My clients were picked up early this morning, and I believe they have no links to al-Qaida"
Abd Allah Hashim,
lawyer for five detainees
In Bahrain, alcohol is sold openly and bars, nightclubs and cinemas attract many foreigners, including Westerners, Saudis and visitors from other more conservative neighbouring Arab nations.
There are fears in the region that Saudi insurgents, under pressure from crackdowns at home might see Bahrain as an easier place to operate with equally attractive targets.
The rash of attacks carried out in the past two months against Westerners in Saudi Arabia has prompted some to look into relocating to Bahrain. From the capital, it's an easy 45-minute commute to al-Khobar, the eastern Saudi oil hub where many foreigners work.
Gulf Arab states signed a security pact in May to improve intelligence sharing to combat what they call "terrorists".