The Contrast Avoidance Model postulates that individuals with generalized anxiety disorder (GAD) fear a sharp spike in negative emotion, and thus, prefer to worry to maintain their negative affect rather than being in a more euthymic state, such as relaxation. Relaxation induced anxiety (RIA) is a paradoxical phenomenon wherein people experience a spike in their anxiety during relaxation training. Because these phenomena may also operate among individuals with major depressive disorder (MDD), we attempted to test whether negative contrast sensitivity was a mediator of GAD or MDD in the prediction of RIA.Individuals with GAD (n = 32), MDD (n = 34), and healthy controls (n = 30) were exposed to a negative emotional contrast by engaging with relaxation practice and then watching a negative emotional video. This was followed by the assessment of their negative contrast sensitivity. After this, participants engaged again with relaxation and RIA was measured. We examined mediation effects of negative contrast on the relationship between the diagnostic status and RIA.Negative contrast sensitivity fully mediated GAD and partially mediated MDD in predicting RIA.Our findings support the hypotheses that negative contrast sensitivity is the mediator of both GAD and MDD in predicting RIA. This may have implications for assessment and treatment of GAD and MDD.