If the file or directory has extended attributes, you'll see an @ in the permissions field. For extended security information (ACLs), you'll see a +.
man ls on OS X:
-@ Display extended attribute keys and sizes in long (-l) output.
xattr program can be used to display and manipulate extended attributes. Take a look at what's there before deciding to go while deleting those attributes, though. Definitely take a quick look at the man page for xattr too.
A quick example from some example PHP compromise code I keep around for reference:
$ ls -@l php-compromise.php
-rw-r--r--@ 1 user group 502620 Jul 5 2011 php-compromise.php