At least 20 others were injured in seven bomb blasts on Sunday.
Minister of State for Home Affairs RPN Singh said National Investigation Agency (NIA) and National Security Guards (NSG) teams have been dispatched for Bihar.
"We have dispatched NSG,NIA teams to Patna. Sadly, Bihar government has confirmed to us that 5 people have been killed in the blasts. Appeal for calm at this time," RPN Singh tweeted.
One person was killed as a crude bomb exploded in Patna railway station earlier in the day.
It was the first blast that rocked the city ahead of Modi's 'Hunkar Rally' in Patna.
Other blasts occurred around Patna's Gandhi Maidan where large number of people had gathered to attend the rally.
Prime Minister Manmohan Singh on Sunday condemned the serial blasts that rocked Bihar's Patna city and left one person dead.
Manmohan Singh spoke to Bihar Chief Minister Nitish Kumar over telephone and asked him to investigate the matter.
He urged the people of the state to maintain peace and calm.
"Prime Minister condemns the blasts which occurred at several places in Patna today. He appeals to the people to maintain peace and calm," the Prime Minister's Office (PMO) tweeted on Sunday.
"PM Dr Singh talks to Bihar Chief Minister Shri Nitish Kumar and asks him to speedily investigate the blasts, and punish the perpetrators," it said.
Meanwhile, Narendra Modi, who did not speak about the blasts while addressing the rally in Patna, later tweeted: "Blasts in Patna are deeply saddening and unfortunate. Condolences with families of deceased and prayers with injured. I appeal for peace and calm."
Senior BJP leader Sushma Swaraj condemned the blasts and said it was a result of 'gross' intelligence failure.
"I strongly condemn serial bomb blasts on the occasion of BJP rally in Patna. This is gross intelligence failure," Swaraj tweeted.
The police have detained one person so far.
--IBNS (Posted on 27-10-2013)