Candido Conde-Pumpido, the state prosecutor, said: "These activities cannot be tolerated and if the police discover them, it seems correct that the judge should order an intervention."
Banned party
Those detained included members of Ekin, a group suspected of being behind violent street protests, and political party ANV, which has stood in local Basque elections but is suspected of having ties to Eta.
The party's leader, Arnaldo Otegi, has been in jail since June on terrorism charges.
In a separate incident, suspected Eta member Juan Carlos Iriarte Perez, 36, was arrested in Hendaye, France, the interior ministry said.
Batasuna was outlawed by Spain's supreme court in March 2003 on grounds that it was the political wing of Eta, which has been blamed for more than 800 killings in bombings and other attacks since the 1960s in a campaign to establish an independent Basque state from parts of northeastern Spain and southwestern France.
Eta called off a ceasefire after peace talks with the Spanish government broke down. Its last major attack took place in December 2006, when a bomb at Madrid airport killed two people.