Mouse-dynamics-related schemes have been shown to be feasible for user authentication systems, however, the existing approaches are either intrusive or not prompt response. Preventing unauthorized accesses to critical digital assets, namely, data stored in the file management system, is one of the major objectives of user authentication. We therefore propose a non-intrusive approach capable of verifying a user having performed a few times of file-related operations via a mouse. To evaluate the effectiveness of the proposed approach, the mouse movement of the file-related operations in Explorer, which is the most common way to search, open, save, copy, and/or delete files in Windows environments, is used for authentication. The experimental results show that the proposed approach is feasible and has three advantages: 1) it is non-intrusive, 2) it authenticates users in a short period of time, and 3) the quantity of mouse dynamics used for authentication purpose is lightweight.