A spokesman for the military command centre in the eastern German city of Potsdam said the explosive attack occurred overnight on a Dingo armoured vehicle and that the two seriously wounded would be evacuated to Germany soon.
The daily Bild newspaper reported in its online edition that the explosive had gone off on the side of a road but it was not immediately clear whether it was a bomb or a mine.
Germany has about 3,000 troops serving with NATO's International Security Assistance Force.
ISAF draws its 47,000 troops from 39 countries. It is helping the Afghan government restore security in the face of an insurgency by the hard-line Taliban movement, which led the country between 1996 and 2001, and push development.
More than 30 international soldiers have been killed this year, most of them in hostile action.
Germany has been under pressure by NATO allies to send combat troops to the south of the country, where the insurgency has been most deadly, but Berlin has said it plans to continue its focus on reconstruction in the north.