The sources said the drone, apparently American, hit the fighters last evening as they rode a motorbike through the Sawmaa area of central Baida province.
The region is a stronghold of Al-Qaeda in the Arabian Peninsula (AQAP), which has taken advantage of the chaos caused by more than two years of civil war to expand its presence in Yemen.
Baida was the site of the first raid ordered by US President Donald Trump after he took office in January.
The Pentagon says it has carried out over 70 air strikes in Yemen since February 28.
More than 7,700 people -- most of them civilians -- have been killed in Yemen's war since a March 2015 military intervention by a Saudi-led coalition against Shiite Huthi rebels, the World Heath Organization says.