Police also targeted three suspects believed to belong to a radical group known as 'mg' behind 25 attacks since 2001.
About 100,000 demonstrators are expected to gather in the area near the summit venue, a hotel in Heiligendamm on Germany's Baltic Coast, from June 6-8.
Authorities are building a 12km-long security fence to separate the demonstrators from the leaders attending the summit.
Attac, an anti-globalisation group, said the raids were "an attempt to criminalise the entire spectrum of G8 opponents."
Wolfgang Schaeuble, Germany’s interior minister, announced that the visa-free travel policy for the Schengen region, which encompasses 13 EU member states and Norway and Iceland, would be suspended for the duration of the summit.
Security concerns were raised last December when opponents of the summit claimed responsibility for torching the car of a German finance ministry official in Hamburg.
Several G8 summits in recent years have witnessed violence. An anti-capitalist protester was killed in 2001 in the Italian city of Genoa in 2001.
Demonstrations at recent G8 summits have been kept well away from the venue although violence has broken out in nearby towns.
The leaders of Britain, Canada, France, Germany, Italy, Japan, Russia and the US will attend the Heiligendamm summit.