A computer enclosure includes a rear plate defining a through opening therein, a mounting bracket secured on the rear plate to cover the through opening of the rear plate, and an interchangeable I/O plate. The mounting bracket includes a top wall perpendicular to the rear plate and, a front wall parallel to the rear plate. The top wall forms an engaging tab thereon. The front wall defines a through opening therein corresponding to the through opening of the rear plate. The I/O plate is configured for covering the through opening of the front wall of the mounting bracket, and defines a securing hole therein for receiving the engaging tab of the mounting bracket. A locking piece is formed on the I/O plate and together with the I/O plate sandwiches an edge of the through opening of the mounting bracket therebetween.