Al-Bab was ISIS' last significant holdout
between the northern countryside of Aleppo and Raqqa, the group's de facto capital. Held by ISIS since 2013, al-Bab was recaptured after more than two months of fighting.
The attack in Sousian village, a few miles north, killed between 53 and 60 people, according to activist groups Aleppo Media Center and the UK-based Syrian Observatory for Human Rights.
ISIS claimed responsibility for the attack in an online statement.
Turkey's state-run Anadolu news agency reported that 60 people were killed and at least 100 others wounded, adding that the car bomb targeted a security building for the Free Syrian Army, an association of rebel groups fighting ISIS.
Dozens of Syrians are being treated at a hospital across the border in the Turkish town of Kilis, Anadolu said.
Thirty-three of those killed in the blast have been identified, said Barry Abdullatif, founder of media activist group al-Bab City Coordination.
There were multiple reports Thursday that Turkish-backed Free Syrian Army rebels had pushed ISIS out of al-Bab, near the Turkey-Syria border.
Turkey's military confirmed in a statement that control had been established in all of the town's neighborhoods.
"Obstructions, mines and IEDs are being cleared in the areas taken under control," the statement said.
Turkey launched a cross-border operation in support of Free Syrian Army forces in August, with the aim of clearing the border area of ISIS fighters and preventing Kurdish People's Protection Unit militias from joining the territories they hold in northern Syria.
Seventy Turkish soldiers have been killed since operation Euphrates Shield was launched.
Al-Bab was bombed by US, Russian and Turkish aircraft this month, CNN reported.