While the error_log files may have read permission, by default they should not be accessible through the web sites they are located within. Public access is restricted by default through specific entries in the Apache configuration (httpd.conf) file; these should be included already and no additional steps may be necessary.
For reference, here are the two specific entries I am referring to:
Code:
<Files ~ "^error_log$">
Order allow,deny
Deny from all
Satisfy All
</Files>
<FilesMatch "^\.ht">
Order allow,deny
Deny from all
</FilesMatch>