While four casualties were reported from Paschim Aurahi Hingna and Purvi Aurahi Hingna villages, one person each died at Pranpur and Kursakatan villages during the storm in Araria district, police said.
Two children below the age of nine were also among the dead in Araria.
A man and his daughter-in-law died at Kursel village in Katihar district as lightning struck their tin-roofed house.
Two deaths were also reported during the thunderstorm from Supaul district, police said.