The page is showing the page title twice, or is displaying the page title and the category title, but the Show Category option is disabled.
Fix this by putting a space in the Page Heading field for the menu item.
- Go to Menus : Select the menu your page is in (Main menu for example).
- Select the menu item for the page you are having the problem with.
- Go to the Page Display tab and put a space in the Page Heading field.
- Save and Close.
The page should only display one page title now. Be sure you have the latest version of Joomla installed, and all your plugins and templates are up to date.