Fear of cancer recurrence (FCR) is a significant risk factor affecting treatment outcomes and prognosis in non-small cell lung cancer (NSCLC) survivors. Behavioral activation (BA), a structured therapeutic approach based on cognitive-behavioral therapy (CBT) principles, has demonstrated efficacy in alleviating psychological distress among cancer patients. This study aims to investigate the effect of BA on FCR in patients with NSCLC and explore the underlying mechanisms. A total of 82 eligible patients were randomly assigned to either the intervention group (BA) (n = 41) or the usual care group (CAU) (n = 41). Assessments were conducted at baseline (T0), week 4 (T1), and week 8 (T2) using the Cancer Recurrence Fear Scale-Brief Form (FCRI-SF), the Hospital Anxiety and Depression Scale (HADS), the Brief Resilient Coping Scale (BRCS), and the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire C30 (EORTC QLQ-C30) version 3.0. Negative emotions (depression and anxiety), as well as resilient coping, were identified as potential mediators. The intervention effect and its potential mediating effects were analyzed using generalized estimating equations (GEE). GEE analysis revealed significantly lower FCR scores in the BA group at weeks 4 and 8 (GroupT1: Wald X = 25.79, P < 0.001; GroupT2: Wald X = 59.59, P < 0.001). Depression and anxiety scores decreased over time in the BA group and remained consistently lower than those in the usual care group (depression: GroupT1 Wald X = 34.67, P < 0.001; GroupT2 Wald X = 56.05, P < 0.001; anxiety: GroupT1 Wald X = 36.22, P < 0.001; GroupT2 Wald X = 64.85, P < 0.001). Scores for resilient coping and quality of life increased over time in the BA group and were significantly higher than those in the usual care group (resilient coping: GroupT1 Wald X = 19.49, P < 0.001; GroupT2 Wald X = 66.19, P < 0.001; quality of life: GroupT1 Wald X = 19.86, P < 0.001; GroupT2 Wald X = 64.46, P < 0.001). Furthermore, negative emotions (depression and anxiety), as well as resilient coping, were found to mediate the effect of BA on changes in FCR. The BA intervention can alleviate FCR symptoms and improve the quality of life in NSCLC patients by reducing negative emotions (depression and anxiety) and enhancing resilient coping.