Invisible a selected category in main page

[fdls]

@Solutho thanks for your help I am trying now but can tell me where should I use this code.

I guess you need to include that in the functions.php or index.php

[Solutho]

Usually it's a bad idea to mess with the core files. Do your tweaks inside the theme.
About the page to edit, usually is at the beginning of the index.php inside the theme folder, but can be in the header. Depends on how the theme is coded.

Either way it's pretty easy to find the loop, just look for ?wp_list_categories? on those files.