The relationship between subclinical coronary atherosclerosis and lipoprotein(a) (Lp[a]) in asymptomatic people with and without diabetes mellitus (DM) is not well understood. We conducted a retrospective analysis of 7201 asymptomatic people (average age 54.4 ± 7.9 years; 65.3% male) who voluntarily had coronary computed tomography angiography (CCTA) as part of a general health evaluation and had no history of coronary artery disease (CAD). The severity and extent of subclinical coronary atherosclerosis were assessed using CCTA, with obstructive CAD defined as a diameter stenosis of at least 50%. Based on their Lp(a) levels, the study participants were divided into tertiles. To assess the relationship between Lp(a) levels and subclinical coronary atherosclerosis, logistic regression analysis was used. In participants without DM (n = 6252), after adjusting for cardiovascular risk factors, there were no statistically significant differences in the adjusted odds ratios (ORs) for calcified plaque, mixed plaque, non-calcified plaque, and obstructive CAD in the third Lp(a) tertile compared to the first tertile (p > 0.05 for all). On the other hand, in participants with DM (n = 949), there were no statistically significant differences in the ORs for calcified plaque (1.117, 95% confidence interval [CI] 0.794-1.572), mixed plaque (1.552, 95% CI 0.888-2.714), or non-calcified plaque (1.735, 95% CI 0.980-3.072) between the first and third Lp(a) tertiles. However, the adjusted ORs for obstructive CAD (2.051, 95% CI 1.248-3.372) were significantly higher in the third Lp(a) tertile compared to the first Lp(a) tertile. In asymptomatic individuals with DM, higher Lp(a) levels were associated with obstructive CAD, which may be linked to an increased risk of cardiac events.