The attack occurred in the morning after two mortar rounds fired by militants struck near the provincial government office building where a celebration was underway.
“Two children and a man were killed and 49 others wounded by the mortar shelling in Asadabad this morning,” provincial Governor Wahidullah Kalimzai told Xinhua.
He blamed the enemies of Afghanistan, a term referring to the Taliban militants for the attack in the mountainous province, 185 km east of Afghan capital of Kabul.
Kalimzai condemned the attack and the Taliban has yet to make comments.
The war-torn Afghanistan on Thursday marked the 97th anniversary of its independence from the British occupation by holding meetings and celebrations across the country amid tight security.
In Kabul, an army officer and his child were injured after a sticky bomb attached to his armored vehicle was detonated in the central part of the city, causing panic among the residents.
The injured were shifted to a nearby hospital in Kolola Pushta locality of the city.
Some 1,600 civilians were killed and more than 3,560 others wounded in conflict-related violence and Taliban-led attacks in the first half of the year, according to UN officials in the country.