Yes, you certainly can and many people do. A belt isn't necessary to perform a huge lift such as a one-rep-max squat, provided you have perfected your form and are properly prepared. If done with bad form, squats can lead to back pain and even injury. However, if you have steadily worked your way up to a heavy weight by maintaining proper form throughout your training, then you can absolutely squat heavy without a belt. That being said, some people appreciate the reassurance and added support of a lifting belt.