The medical charity told Reuters it had lost contact with some of its staff in Yemen and that it could not share more details at this time out of concern for their safety.
The security source said the employees were a German and a Mexican and were taken from their car by gunmen that security forces believed to be linked to Al Qaeda in the Arabian Peninsula.
Islamist militant groups are among many destabilising forces in war-torn Yemen which is grappling with a humanitarian crisis.
In February, five United Nations staff, including four Yemenis, were abducted in Abyan governorate by gunmen also believed to be linked to Al Qaeda. read more
The militant group operates in south and eastern regions of Yemen, which has been divided by a seven-year war between the Saudi-backed government based in the south and Iran-aligned Houthi movement in the north.
Al Qaeda took advantage of 2011 Arab Spring chaos in Yemen and the ouster of a transitional government from the capital, Sanaa, by the Houthis in 2014 to create mini states, but was driven back following the intervention of a Saudi-led coalition in the war against the Houthis.