This study examined the relationships between motivational beliefs, defined as self-efficacy for self-regulated learning and achievement goals, engagement and academic cheating in the context of learning biology. Gender differences across these variables were also examined and both active and second-party types of cheating were included. Based on the hierarchical model of achievement motivation, we hypothesized that achievement goals and engagement would play a mediating role between self-efficacy for self-regulated learning and academic cheating. Participants were 283 high school students from Croatia. Data were collected using (1) the Self-Efficacy for Self-Regulated Learning Scale, (2) the Achievement Goals Scale (subscales: mastery-approach, mastery-avoidance, performance-approach, performance-avoidance, work-avoidance), (3) the Engagement in Learning Biology Scale (subscales: behavioural, cognitive, and emotional engagement), and (4) the Academic Cheating Scale (subscales: active and second-party cheating). The results demonstrated that girls exhibited higher self-efficacy for self-regulated learning, mastery achievement goals, and engagement, while boys exhibited higher work-avoidance goals. No gender differences were found in academic cheating. Mediational analysis revealed that behavioral engagement was a mediator between self-efficacy for self-regulated learning and active cheating. The findings of the present study demonstrate the importance of motivation and engagement in understanding academic cheating and in preventing this unethical behavior.