The army on April 11 ousted Sudan's longtime leader Omar al-Bashir after a months-long protest movement.
A military council which took power has so far resisted calls from protesters to quickly bring in a civilian administration.
On Thursday, exactly four months since protests started, roads leading to the sit-in area were packed with crowds flocking to the army headquarters.
Activists mobilized demonstrators through social media to keep up the pressure for replacing the military council, now led by General Abdel Fattah al-Burhan, AFP reported.
"Power to civilians, power to civilians," protesters chanted through Thursday night.
"I won't leave until Burhan transfers power to a civilian government," said Wali Aldeen, who has camped outside the complex since the day Bashir was ousted.
Activists have called for large crowds to gather after the weekly Muslim prayers, as on previous Fridays.
Protests first broke out on Dec. 19 in response to the tripling of bread prices, swiftly turning into nationwide rallies against Bashir's three-decade rule.
After his ouster, protesters demonstrated against General Awad Ibn Ouf who took over as the first head of the military council, insisting he was a close aide of Bashir and a top regime figure.
Ibn Ouf stepped down in less than 24 hours and was replaced by Burhan, who so far has appeased protesters by lifting a night-time curfew and vowing to "uproot" the Bashir regime.