As building information modeling (BIM) systems continue to be widely adopted, there is an increasing demand for an active construction schedule management system with more advanced decision-making capabilities. For example, if overlapping between construction activities is significant, the performance of construction operations for the corresponding activities may deteriorate. Thus, a viable construction schedule should be formulated in order to minimize overlapping of proximate construction activities. An active system can be regarded as a certain solution for this issue. The purpose of this study is to develop a systematic methodology and computer system for an optimal construction schedule simulation that minimize overlapping activities for the enhancement of a project's operational performance. This study centers on identifying overlapping activities, applying fuzzy theory, and analyzing risk levels for schedule overlap issues. In addition, genetic algorithm (GA) theory is adopted for the minimization of the overlapping of highly risky activities. Finally, an optimal construction schedule that minimizes overlapping activities is suggested. The optimal schedule is visualized in a BIM-based four-dimensional (4D) computer-aided design (CAD) environment. The 4D CAD system developed in this study includes fuzzy and GA analysis functions with a schedule simulator. A case study on an actual project is introduced to validate the effectiveness of the proposed methodology.