However, the sources said the arrests on Wednesday were not related to the 11 March attacks in Madrid that left nearly 200 people dead.
"An operation was launched against Islamic activists and several people were detained," a spokesman for Catalonia regional police said.
Judicial sources in Madrid said the suspects were arrested "for Islamic terrorism" and said all were of Pakistani origin.
A police spokesman said the Pakistani suspects "could have financed radical organisations outside Spain's borders."
Judicial sources said they were sifting through documents to determine "the contours and the methods pertaining to this collaboration."
The sources in Madrid said police had not discovered any weapons or explosives but only documents including false identity papers as well as "books on (al-Qaida leader Usama) bin Ladin."
"An operation was launched against Islamic activists and several people were detained"
Catalonia regional police
Five of the Pakistanis were detained in the northern Barcelona district of Trinitat Vella and five more in the central "Barrio chino" or Chinese district, where there is a concentration of Pakistanis.
Sixteen suspected Islamic anti-government activists from North Africa were arrested in the Catalonia region of eastern Spain in January last year but released for lack of evidence three months later.
Four Algerians were arrested once more and charged last March with belonging to the country's anti-government Salafist Group for Preaching and Combat (GSPC), a sub-section of the Islamic Armed Group.