Munir Ahmad Farhad, the spokesman for the governor of Balkh province, said the civilians were killed by unidentified gunmen who stopped their vehicles and then shot them dead.
The incident took place as Ghani opened a conference of donors to his country's reconstruction after almost 40 years of war, telling them he has made progress on a range of major challenges including security and corruption.
Ghani told the meeting his government has accelerated a crackdown on corruption, reformed customs to significantly increase revenue collection and boosted capacity building.
He acknowledged a problem with job creation but said it was a "priority of the national unity government."
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He noted he has also sought to bring women into senior government positions, including four ministers and one provincial governor.
The one-day meeting followed a two-day Regional Economic Cooperation Conference on Afghanistan, which brought together officials from more than 30 nations and 40 international organizations.
Afghanistan's economy has been in decline since international military and charities began withdrawing, with most combat troops out by the end of last year, bursting the bubble created by the massive inflow of military and aid cash.
The World Bank has predicted 2.5 per cent GDP growth this year, after averaging 9 per cent a year from 2003 to 2012.
Ghani came to power a year ago promising to bring peace and prosperity, and made pledges at a summit in London in December aimed at reassuring donors he had reform plans that would move the country away from the culture of corruption that prevailed under his predecessor Hamid Karzai. Now Ghani is delivering a progress report on those plans.
"We recognize that we need to send a sharper, clearer signal to investors that this government is serious about growth," Ghani told the gathering.