There was no immediate link between the two-car bombings near Al-Bab and in Afrin that killed a total of eight people, or the incident that claimed 21 lives in a minefield, France24 reported.
In the first incident, explosives planted in the car of a police chief on the outskirts of Al-Bab detonated and killed him, two other policemen and two civilians, said the Syrian Observatory for Human Rights.
Nineteen people were wounded, the Britain-based monitor added.
An AFP photographer saw the charred, mangled remains of a vehicle at the site of the explosion.
In the town of Afrin, a car bomb went off near a bakery, killing three people and wounding 16 others.
There was no immediate claim of responsibility for either blast.
There has been a string of attacks in Al-Bab since its capture by Turkish troops in 2017.
Several have also hit Afrin, which Turkey and its Syrian forces seized from Kurdish fighters in 2018.
Elsewhere in north Syria, a number of pro-Turkey fighters were killed overnight near the town of Ain Issa when they walked into a minefield laid by Kurdish-led forces, the monitor said.
They were among around 30 Turkey-backed combatants who had been trying to sneak into Muallaq village after sending in drones to bombard it, said the Observatory.
But they became ensnared in a minefield laid by the US-backed Syrian Democratic Forces (SDF), killing 21 and wounding the rest.
Since then, pro-Ankara fighters have been stationed to the north of Ain Issa, and sporadic skirmishes have broken out between them and SDF.
MNA/PR