Fear of cancer recurrence (FCR) represents one of the most frequent and clinically meaningful psychological problems among individuals living with and beyond cancer. Rather than reflecting a simple emotional reaction, FCR is increasingly recognized as a complex biobehavioral condition shaped by symptom perception, maladaptive cognitive processing, behavioral avoidance, chronic stress responses, and wider survivorship challenges. Cognitive-behavioral, mindfulness-informed, and psychoeducational interventions remain the best-established strategies for FCR management. Exercise should therefore be understood not as an independently proven cure for FCR, but as a potentially useful adjunctive strategy that may target several behavioral and physiological processes involved in recurrence-related fear. This narrative review synthesizes current evidence and theoretical pathways regarding the role of exercise in FCR management from behavioral, psychoneuroimmune, and digital-delivery perspectives. At the behavioral level, exercise may reduce vulnerability to FCR by improving self-efficacy, restoring perceived control, improving sleep and fatigue, reducing catastrophic interpretation of bodily sensations, and promoting behavioral activation and social connection. From a psychoneuroimmune perspective, FCR may be associated with chronic threat vigilance, autonomic imbalance, stress-related neuroendocrine dysregulation, and inflammation-related symptom clusters; however, these pathways remain partly inferential, and few clinical trials have simultaneously measured FCR outcomes and biological biomarkers in exercise interventions. Digital health platforms, smartphone-based programs, wearable devices, telecoaching, and online exercise formats may increase scalability and long-term support, but they also raise issues of digital literacy, access, and equity. Overall, exercise is best positioned as an adjunct component of stepped-care, multimodal, and technology-supported FCR-targeted survivorship care. Further randomized trials with FCR as a primary endpoint and embedded mechanistic assessments are required.