BNP leaders and activists started gathering in front of the party's Nayapaltan headquarters in the capital from the morning.
The rally is scheduled to begin at 2:30pm, as previously announced, in observance of International Democracy Day.
Thousands of the party leaders and activists are seen chanting slogans in favour of BNP.
The party members from different wards have been going to join the rally in brief processions wearing coulourful caps and carrying placards and posters.
However, senior party leaders are yet to reach the venue, reports our correspondent from the spot.
Acting Chairman Tarique Rahman is expected to address the rally as the chief guest, with BNP Secretary General Mirza Fakhrul Islam Alamgir and other senior leaders scheduled to speak.
A monitor has been set up in front of the stage to broadcast his speech virtually.