It doesn't work like on the computer, but you can set favorite channels, then only display your favorite channels when pushing the Guide button.
http://customer.xfinity.com/help-and-support/cable-tv/x1-guide-add-a-channel-to-favorites
http://customer.xfinity.com/help-and-support/cable-tv/x1-guide-filter-your-guide
Lastly to make Favorites the default view: Xfinity button - Settings (Gear Icon) - Comcast Labs - Default Guide View (choose Favorites)