Facebook comments can be moderate directly on the site where the comments are displayed, see image:
Or you can administrate and moderate the comments on Facebook page: http://developers.facebook.com/tools/comments
To be able to moderate the comments, you need to be set as moderator in the Facebook application settings. On the site listed above, select the application which is assigned to Facebook comments and click on Settings.
Select Facebook user as an moderator and click save to store the settings. Then you will be able to moderate the Facebook comments.