Quoting a statement from the provincial governor's media office, TOLOnews reported that the explosion took place in the afternoon and was intended for a convoy of the Afghan armed forces. However, the blast affected the civilians who were travelling on the highway.
No Army personnel suffered casualties during the attack while they were passing through the area, the statement said.
Four civilian vehicles were damaged in the suicide blast.
The attack came hours after a car suicide bombing in capital Kabul killed 10 people, including a US and a Romanian service member and left 42 others injured.
The incident took place at around 10:10 am (local time) near the National Directorate for Security (NDS) checkpoint in Kabul's Police District 9, according to the Afghan Interior Ministry.
The Taliban had claimed that the attack targetted a foreign forces convoy, which was entering an NDS facility in the heavily-guarded Shashdarak area, home to several important buildings including the headquarters of NATO-led forces in Afghanistan, the Afghan Defence Ministry and the CIA's Afghan station to name a few.
The latest attacks have come even as US envoy on Afghan peace reconciliation, Zalmay Khalilzad, has been meeting Afghan President Ashraf Ghani and briefing him on the agreement that was reached "in principle" with the Taliban following the completion of the ninth round of talks in Doha last month.
The agreement aims at ending the nearly two-decades-long civil war in Afghanistan.
The Afghan government was until now shut out of the negotiations as the Taliban calls it a "puppet" of the US.