No further details were released about the arrested but the police said that there was no threat to public safety.
Dzokhar Tsarnaev, a 19-year-old student, has been accused over the blasts. His elder brother, Tamerlan, 26, was killed during a shoot-out with the police while they were escaping after shooting a police officer dead at the Massachusetts Institute of Technology four days after the deadly blasts.
Dzokhar, who was seriously injured at the time of the arrest, has been accused of using a weapon of mass destruction and destruction of property resulting in casualties. He could be sent to the gallows if convicted of the first charge.
During interrogation, Dzokhar said that he and his dead brother were disgusted by the US wars in Iraq and Afghanistan and sought to defend Islam.
The Tsarnaev family originates from the predominantly Muslim republic of Chechnya in southern Russia. The brothers had been residing in the US for about a decade. Dzokhar is a US citizen while Tamerlan was in the country on a Green Card.