Bahrain's interior ministry said in a statement that the four were arrested in Sitra, a Shia-majority village south of the capital, Manama, which has repeatedly seen anti-government protests.
The four had entered the country between 11 and 12 February and one of them was a woman, it said.
"At least some of the arrestees were in the country as members of the international media but had not registered with the concerned authority and were involved in illegal activities," the statement said.
One of the detained was "wearing a mask and participating in attacks on police alongside other rioters in Sitra", the statement added. The other three were arrested at a security checkpoint in the same area.
Bahrain has been wracked by political unrest since an uprising in 2011, with the kingdom's Shia majority demanding greater political rights from the Sunni-led government. Some violent attacks have blamed on militants linked to Iran.
The violent suppression of the protests left dozens killed, hundreds injured and many more arrested.