This study examined the influence of frailty status and physical activity (PA) compliance on all-cause mortality and healthcare utilization among Korean adults aged 45 years and older. Data from 2104 participants in the Korean Longitudinal Study of Aging (KLoSA; 2006 - 2022) were analyzed. Frailty was assessed using a 38-item frailty index (FI), and PA was defined according to adherence to the World Health Organization guideline of at least 150 min per week. Participants were classified as robust, pre-frail, or frail. Cox proportional hazards models and generalized linear mixed models were used to evaluate associations with mortality and healthcare utilization. Compared with robust individuals, frail participants exhibited a markedly higher risk of all-cause mortality (hazard ratio [HR] = 3.37, 95% confidence interval [CI]: 2.42–4.69), while pre-frail individuals also showed an elevated mortality risk (HR = 1.72, 95% CI: 1.43–2.07). Frailty was consistently associated with greater healthcare utilization across outpatient visits, hospital admissions, length of hospital stay, and healthcare costs. Adherence to PA guidelines was not independently associated with reduced mortality among pre-frail and frail individuals after multivariable adjustment; however, a significant interaction indicated higher healthcare costs among frail individuals who met PA guidelines. In addition, higher BMI was associated with lower mortality risk, consistent with patterns described as the obesity paradox. These findings highlight frailty as a key, independent predictor of mortality and healthcare utilization beginning in midlife. Standardized PA recommendations alone may be insufficient for physiologically vulnerable populations, underscoring the importance of early frailty screening and individualized, function-sensitive intervention strategies to promote healthy aging.