The casualties were reported from Saharsa, North Darbhanga, East Champaran and Samastipur districts of the state.
"In Bihar, death toll from thunderstorms and lightning has risen to 27. Maximum eight deaths have been reported from Saharsa district," an official posted in Patna said, Xinhua news agency reported.
According to India's state-run broadcaster All India Radio, the local government has announced a compensation of 5,923 US dollars to each family that lost its member in the calamity.
Reports said crops, including mango, litchi, and maize, have been damaged due to the storm.
Meanwhile, meteorological department officials have forecast thunderstorms and lightning in the next 48 hours in several parts of the state.
Last month, dust storms and thunderstorms accompanied by rains killed over 250 people and injured more than 400 in five states in the country.