Objective: This paper applies Reinforcement Sensitivity Theory to explain the role of exposure to violent extremist content online in the wider psychological process of “radicalization.” Reinforcement Sensitivity Theory is a suitable theory to apply to this domain given that (a) the motivation to engage in violent extremism is widely discussed, yet motivational theories are rarely applied and (b) current risk factors for engagement in violent extremist behavior show a high degree of overlap with core Reinforcement Sensitivity Theory variables (e.g., impulsivity and social dominance). Method: This study uses an experimental design in which 479 participants from Amazon’s Mechanical Turk were randomly assigned one of two short vignettes (violent extremist/violent nonextremist) to frame the content of a social media-based behavioral task. The effect of exposure to violent extremist content online on intentions for political mobilization was measured via the Activism and Radicalism Intentions Scale. Results: While exposure to online violent extremist content did not increase tendencies for political mobilization, Behavioral Activation System traits were positively associated with the willingness to engage with violent extremist content online and with intentions for political mobilization. Conclusions: Behavioral Activation System traits provide a possible avenue to explain individual differences in the process of radicalization and the potential relevance of Reinforcement Sensitivity Theory for theories of radicalization provides further evidence that new knowledge that can be gleaned by applying established psychological theories to the study of radicalization.