"Wait for August 18; it will be an important day for Bihar when the prime minister will announce a special package for the state," Mr Pradhan told the media in Patna.
"Modi has promised a special package of more than Rs 50,000 crore to Bihar for its development," he said.
Mr Pradhan said Mr Modi would fulfil the promises he made during the 2014 Lok Sabha election campaign and at a rally in Patna in 2013.
According to Mr Pradhan, the Prime Minister will formally announce a special package for Bihar either at Ara or Saharsa.
Mr Modi will also lay the foundation stone of a four-lane road connecting Patna and Buxar in Ara, the district headquarters of Bhojpur, about 60 km from Patna, before addressing the Bharatiya Janata Party rally in Saharsa district in flood-prone Kosi region.
Mr Modi has already addressed two election rallies in Muzaffarpur and Gaya ahead of the Bihar Assembly polls.
Bihar Chief Minister Nitish Kumar has repeatedly demanded a special category status for Bihar and said anything less won't help it develop.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.