According to al-Sumaria news website, the source said Iraqi security sources managed to track and detain the suspect soon after the blast.
The individual was arrested in a nearby restaurant.
Another source at the Iraqi interior ministry said the suspect had gotten on the minibus at Jarf al-Sakhra district and left an exclusive device in the vehicle before getting off.
Minutes later, the device went off at the checkpoint 54 on the road between Baghdad and Karbala.
At least 12 people were killed and several others wounded in the bomb attack.
They said the wounded were rushed to a nearby hospital. There was no immediate claim of responsibility for the blast.
“Twelve civilians have been killed and five wounded in an explosion on a bus at the main checkpoint for the northern entrance to Karbala”, the city's health authorities separately said.