Background: Obstructive sleep apnea (OSA) is associated with increased cardiovascular morbidity; however, its relationship with subclinical coronary atherosclerosis detected incidentally on routine chest computed tomography (CT) remains incompletely defined. We aimed to evaluate the association between questionnaire-based OSA risk and moderate-to-severe coronary artery calcification (CAC) in patients without known cardiac disease undergoing non-contrast chest CT for non-cardiac indications. Methods: In this prospective cross-sectional study, 268 consecutive adults undergoing routine non-contrast chest CT were included. OSA risk was assessed using the Berlin Questionnaire (BQ) and a modified BQ (mBQ), excluding hypertension and obesity components. CAC was quantified using the Agatston method on non-gated CT images, and moderate-to-severe CAC was defined as a score > 100. Multivariable logistic regression models were adjusted for age, sex, smoking status, alcohol use, obesity, lung disease, diabetes mellitus and hypertension. Results: Moderate-to-severe CAC was substantially more prevalent among patients at high risk for OSA than among those at low risk (43.1% vs. 12.0%, p < 0.001). In unadjusted analyses, high-risk OSA was strongly associated with CAC > 100. After multivariable adjustment, BQ-defined high-risk OSA remained independently associated with moderate-to-severe CAC (adjusted odds ratio [OR] 2.74, 95% confidence interval [CI] 1.29–5.78, p = 0.008). Similar results were observed with the mBQ (adjusted OR 2.62, 95% CI 1.27–5.41, p = 0.009). Increased snoring intensity was also independently associated with CAC > 100 (adjusted OR 2.25, 95% CI 1.07–4.72, p = 0.032). Conclusions: Questionnaire-defined high-risk OSA is independently associated with moderate-to-severe incidental CAC detected on routine chest CT. These findings support the integration of sleep-related risk assessment into opportunistic cardiovascular imaging frameworks and highlight the potential role of thoracic CT in multidimensional cardiovascular risk stratification.