“The blast ripped through the main square of Faizabad city in Kishim district,” Xinhua news agency quoted a provincial government official as saying.
The explosive was attached to a motorcycle in the crowded circle, the official said.
The injured were shifted to nearby hospitals.
“Majority of the affected people were local vendors while several women and children were among the injured. Many shops around the site were also damaged,” he said.
No group has claimed responsibility for the attack yet.
The explosion was the third bomb attack in the country within a day.
At least 14 Nepali security guards were killed and nine injured after a suicide bomber struck a bus in Kabul on Monday morning.
The attack in Kabul was followed by a roadside bombing which injured five people, including a provincial council member, in the city.
Taliban militant group has claimed responsibility for the Kabul bombings.
The Taliban-led insurgency has been rampant since early April when the militant group launched its annual rebel offensive in different areas of the country.
About 600 civilians were killed and more than 1,340 wounded in conflict-related violence and Taliban-led attacks in the first quarter of the year, according to UN mission in the country.