There are several ways to use the RadCheckBoxList via the keyboard only:
Set its TabIndex property and use the Tab key to navigate to the desired item and then press the Enter or Space key to select it.
Set its AccessKey property. This allows you to use the browser's shortcut combination to select the first item in the checkboxlist ("Alt + AccessKey" in IE and Chrome, "Shift + Alt + AccessKey" for Firefox, "Shift + Esc + AccessKey" for Opera).
Note: By default, tab-access is disabled in Safari. To enable it, check "Preferences > Advanced > Press tab to highlight each item on a page".