I would say it depends on what you're doing CGI with. Writing CGI scripts in Perl would be on topic, but problems you might be having with your PHP CGI scripts wouldn't. Similarly if you using a Perl script to generate HTML, or using the Perl DBI to access your database that would be on topic too, but doing the same tasks in another language wouldn't be.

This is a Perl forum. If the problem involves Perl it is probably on topic (or at least people will tell you, generally politely, why it's off topic and what to search for/where you might be able to find suitable help). Anything completely un Perl-related is obviously off topic.

Update: fixed a small typo, thanks jeffa :)