In the video that was sent to Austrian broadcaster ORF, a group calling itself the Global Islamic Media Front also demanded that Austria release two Islamists detained in Vienna.
"The mujahedin have spared you (Germany and Austria) so far, therefore the number of dead soldiers is not particularly high. But this will now change," the video's German subtitles say.
While Germany has more than 3,000 soldiers stationed in Afghanistan, Austria has only three military advisers working in Afghanistan.
German Interior Minister Wolfgang Schaeuble said Berlin would take the threats "seriously" but added that no re-evaluation of the Islamist terror threat was needed.
A similar video authored by the same group was aired in March; Austrian police in September detained a young couple believed to have produced the group's first threat video. Just days after the couple's arrest, however, a new Islamic Web site managed by the Global Islamic Media Front surfaced.
Berndt Georg Thamm, a German terrorism expert, said the Global Islamic Media Front is made up of a group of people determined to disseminate al-Qaida's ideology over the mass media.
"They are no armed (terrorists), but ideological combatants," he told German news channel n-tv on Wednesday.