It comes a day after clashes broke out at a rally in support of Qadri, who was executed last month for the 2011 murder of reformist politician Salman Taseer.
There were new clashes on Monday as police made a number of arrests and cleared some areas of protesters.
Qadri killed Mr Taseer over his opposition to strict blasphemy laws.
His supporters say he is a hero and should be considered a martyr.
Critics say the blasphemy laws, which allow the death penalty to be imposed in some cases, are often misused to oppress religious minorities.
The protest was not given much prominence in local media, which is increasingly under official pressure to tone down coverage of events that might encourage unrest.
The BBC's M Ilyas Khan in Islamabad says protests are now concentrated in the so-called Red Zone of the capital, home to parliament and many government buildings.
Reports put the number of demonstrators at several thousand.
Sunday's unrest involved an estimated 25,000 people. Police fired tear gas at protesters who threw stones, damaged property and started fires in the street.
Thousands of supporters of executed Islamist killer Mumtaz Qadri are staging a sit-in outside Pakistan's parliament in Islamabad.