Besides party workers, the former chief minister was joined by dozens of party MPs and legislators at the "dharna" site at the JP roundabout near Gandhi Maidan.
Nitish Kumar said the protest was against the Bharatiya Janata Party-led central government's injustice and betrayal in granting special category status to the state.
JD-U spokesman Neeraj Kumar said party leaders and workers were staging similar "dharna" at all district headquarters across the state "to expose the double talk of the central government".
He said Prime Minister Narendra Modi, who promised special status to Bihar during his campaign for the Lok Sabha polls, has betrayed the people of Bihar after getting their overwhelming support.
"Modi had promised to provide special status to Bihar after being elected to power. But he has not only forgotten his words, his government is discriminating in providing funds meant for development and implementation of welfare schemes," Neeraj Kumar said.
He alleged that the central government had cut fund allocations to Bihar in schemes like Sarva Shikhsha Abhiyan, Mahatma Gandhi National Rural Employment Guarantee Act, Indira Awas Yojna and other central sponsored schemes.
Last week, Nitish Kumar said on Facebook that the time has come for the people of Bihar to seek "hisab" (account) from the BJP over its betrayal.
"People of the state will take them to task for injustice and betrayal over providing special category status to the state," he wrote.
Nitish Kumar has already made it clear that the special category status would be his main plank in the next year's assembly elections.