The current study investigates the role of individual and intergroup factors in predicting Muslims’ tendency to attribute domestic terrorism in Indonesia to an external cause (i.e., The West) or an internal cause (i.e., radical Islamist groups). The results (N = 308) showed that intergroup factors of symbolic threat and realistic threat directly increased the external attribution and conversely decreased the internal attribution. Within the context of the current research, symbolic threat refers to Muslims’ perception that the norms and values of the West undermine Islamic identity. Realistic threat denotes Muslims’ perception that the economy and technology of the West undermine Islamic power. The individual factor of Islamic fundamentalism, which has to do with Muslims’ belief in the literal interpretation of and strict guidelines to Islamic doctrines, indirectly predicted both external attribution and internal attribution of terrorism as hypothesized, via the extent to which Muslims perceived the West as posing a symbolic threat, but not a realistic threat to Islamic existence. Uncertainty avoidance, a cultural dimension that describes the extent to which people view clear instructions as a pivotal source of concern to deal with societal problems, also significantly increased perceived symbolic threat and realistic threat, and this cultural dimension mediated the effect of Islamic fundamentalism on each of the intergroup threats. Finally, we found that the level of Islamic fundamentalism was dependent upon cognitive response, but not emotional response to mortality salience. The cognitive response to mortality salience denotes what Muslims are thinking about in coping with their own death whereas the emotional response denotes what Muslims are feeling about such issue. In particular, we found the cognitive response, but not the emotional response to mortality salience significantly gave rise to Muslims’ Islamic fundamentalism. These findings shed light on the importance of combining individual factors and group factors in explicating the dynamics of Muslims’ tendency to make attributions of causes of domestic terrorism. We discuss theoretical implications and study limitations, as well as practical actions policy makers could conduct to deal with Muslims’ Islamic fundamentalism and reduce the extent to which this particular group perceives the West as threatening their existence.