Entirely depending on the location and application you are
using at the instant of the "click," it will vary. The most
common "click" keyboard key is the Enter key. If a program
shortcut is highlighted and you press the Enter key the
program will start. If you have an OK, Close or Cancel
highlighted and press the Enter key that function will
occur.
Don't need to try it since I use the feature all the time so
I don't have to reach for the mouse. Use tab key to switch
highlight and then the enter for activate.