The NIA conducted raids at two places in Lakhisarai Friday night on the basis of information provided by other intelligence agencies, a district police official said.
"In the raid, the NIA detained six people and recovered 300 passbooks, 30 ATM cards and other documents related to money transaction," the official said.
The NIA suspects that those detained have links with terrorists in and outside the country.
"The NIA and intelligence officials have been interrogating the six detained people to get more information," police said.
In the last three days, the NIA has conducted raids at several places in Bihar in search of suspects involved in the serial blasts in Patna Oct 27, police said.
Earlier this week, Bihar Police formally handed over investigation of the serial blasts to the NIA.
The NIA also raided Muzaffarpur and Motihari in search of suspects.
Six people were killed and nearly 100 injured in the serial blasts in Patna ahead of a rally addressed by the Bharatiya Janata Party's prime ministerial candidate Narendra Modi.