The four men - Ahmad Hussain, Fakruddin, Mohammad Raju and Anil Pandey - will be interrogated by the NIA after a special court granted it permission, a police officer said here Friday.
They are currently lodged in Beur Central Jail here and suspected of being linked to the Indian Mujahideen and the Students Islamic Movement of India (SIMI).
"A day after the court allowed the NIA to interrogate the four accused, the probe agency is likely to interrogate them Friday in jail," the police officer said.
The serial blasts October 27, 2013 killed at least six people and injured nearly 100.
The NIA team had arrested Hussain and Fakruddin in February from Mirzapur in Uttar Pradesh and later arrested Raju and Pandey.
The NIA officials suspect that Raju had purchased the explosives - Ammonium Nitrate - from Pandey, a resident of Allahabad.
Earlier, four other people, including main accused Imtiyaz Ansari, were arrested in connection with the serial blasts. Last month, a special NIA court here filed a chargesheet against Ansari.
Ansari, a resident of Jharkhand's capital Ranchi, was arrested at the Patna railway station after a bomb exploded on the platform few hours before the Bharatiya Janata Party leader's rally at Gandhi Maidan here.