Nowadays, some usb devices will act like mice ( for example, headphones that can adjust volume and pause/resume music ). Not all of them are expected to have the right to access qubes.InputMouse.
But, currently there’s no way to determine which device is requesting to send mouse input to dom0. The prompt window shows no info about that.
A possible solution is to add one parameter to qubes.InputMouse request, that implies the name of the device. There may be special rules to auto accept some devices, and deny others.