The rich:calendar component does not allow keyboard navigation by default. Selecting dates are only accomplished by using the mouse. Anyone who knows how to navigate with keyboard in the calendar component?
This is not currently possible with the RF4 calendar. We are looking at replacing the client-side implementation of the calendar in RichFaces 5, perhaps with the jQuery UI datepicker, where it is possible to select the date using the keyboard by holding down the ctrl + arrow keys.