The amount of uploaded extremist propaganda on the internet is increasing. In particular, right-wing extremist as well as Islamic extremist groups take advantage of the opportunities presented by the internet to spread their ideas to worldwide masses. Both tackle in-group specific topics and address their audiences in their respective political, national or religious identities. Several factors, such as higher levels of authoritarian value orientations and threatening life situations (such as existential threats or psychological uncertainty) have been found to shape people’s reactions towards radical groups as well as to propaganda. The current study investigated whether the response to extremist propaganda videos (namely, aversion felt for the video and the perceived persuasiveness of the video) is shaped by an individual’s authoritarian attitudes and psychological uncertainty and whether this is a global process or in-group specific. Further, it considered the effects of exposure to extremist propaganda on the identification with one’s in-group. In a laboratory experiment, German students were confronted with a right-wing extremist and an Islamic extremist video after manipulating their level of uncertainty (high vs. low levels of psychological uncertainty). The results confirmed that the interaction between authoritarianism and psychological uncertainty affected the evaluation of right-wing extremist videos addressing participants’ national in-group. Under conditions of uncertainty, authoritarianism predicted less aversion and a higher persuasiveness of these videos. Further, psychological uncertainty increased the identification with participants’ German nationality, irrespective of authoritarian attitudes. Notably, the effect was in-group bound: The same effect was not found for Islamic extremist propaganda referring to a religious out-group. The results are discussed regarding the potential of propaganda to foster behavioral intentions and engagement in extremist groups in specific threatening situations.