A cocktail blasted near Ganajagaran Mancha at Shahbagh intersection at around 3:30pm, while another cocktail was recovered unexploded from the same scene.
Witnesses said the bomb exploded 5-7 feet from the place where the platform was centred.
There is no report of any casualty or injury during the explosion.
Turning down the International Crimes Tribunal 1 verdict against retired Jamaat-e-Islami ameer Golam Azam, the activists of Ganajagaran Mancha brought out a procession from Shahbagh intersection around 2pm.
They also vandalised two passing vehicles and put barricades in and around Shahbagh area, disrupting traffic.
Earlier in the day, the tribunal sentenced Ghulam Azam, in his early 90s, to jail unto death for crimes against humanity committed during the 1971 Liberation War.