Patna Senior Superintendent of Police Jitendra Rana said the main accused Kundan Kumar was arrested from Ekangalsarai in Nalanda district.
Kundan Kumar is being brought to Patna where Patna police and the National Investigation Agency would jointly interrogate him in connection with the bomb explosion in the Bahadurpur housing colony flat.
With the arrest of the main suspect, the two other absconding accused -- Hemant Kumar and Ashok Kumar -- would be nabbed soon, the SSP hoped.
Explosion of a high intensity bomb had ripped through a flat in MIG Sector 3 of Bahadurpur under Agamkuan police station on March 30 night.
Two other high-intensity live can bombs fitted with timer of Lotus company were defused timely by the police.
Three persons were identified as being behind making of the can bombs.
Recovery of timer of Lotus company in the bombs raised suspicion of security agencies if the incident had any link with the 2013 serial bomb blasts in Patna and Bodh Gaya.
A watch of the same brand was used in the bombs that went off in 2013 at Narendra Modi's rally at Gandhi Maidan ahead of the Lok Sabha polls and at Bodh Gaya same year.
The Anti-Terrorist Squad is also probing Kundan's relations with Haider Ali, a prime accused in serial blasts in 2013 in Patna during then BJP PM candidate Narendra Modi rally.
Additional Inputs: PTI