Xorg binary runs the X desktop. You don't say which version of Ubuntu you're using. You should specify these things in your questions to get better answers. Please edit the question to clarify.
Anyway, if this is not a desktop system and you aren't using any form of graphical desktop environment on it then you could remove the relevant package, which is:
$ dpkg -S Xorg xserver-xorg-core: /usr/bin/Xorg xserver-xorg-legacy: /usr/lib/xorg/Xorg.wrap xserver-xorg-core: /usr/lib/xorg/Xorg xserver-xorg-legacy: /usr/share/man/man1/Xorg.wrap.1.gz xserver-xorg-core: /usr/share/man/man1/Xorg.1.gz
Due to dependencies, removing any of those will want to remove a great deal of other packages too.
However, the fact that it's running and using 40% CPU suggests you actually are using it. If you are using any kind of graphical desktop environment here then it won't be a good idea to try to remove the package for this binary.
If you do need it then it's difficult to work out why it's using so much CPU unfortunately.
If it's always done this, you may need to install drivers for any graphics hardware you have. This answer covers installing additional graphics drivers.
If it's a new symptom, well, it could just be a one-off problem that may be resolved by rebooting. Normally you would only expect high CPU usage on the Xorg process when there is heavy use of video or similar in some window.