I believe that Wordpress will try to find a suitable URL if you enter a wrong one. So I have a page http://www.example.com/products/ and by mistake I enter http://www.example.com/prods/ Wordpress will probably automatically redirect.
I think that it is similar to the Multiviews option in apache. Can the Wordpress features be turned off?
WordPress doesn't automatically suggest pages when a 404 occurs. Many themes have a 404.php template file that can effect what happens when an incorrect URL is entered. Maybe your theme has a 404 page. If you don't want it to interfere, you could try deleting the 404.php.
REVISION:
OK, I understand your request now. The best I've been able to come up with is to add this to the functions.php file:
<?php remove_action( 'template_redirect', 'redirect_canonical' ); ?>
This is probably not a good idea, I'm sure it handles more than just suggesting a page when the URL given is a close match. If you want to mess around with the code to see what you can come up with, you can find it canonical.php core file located in wp-includes/canonaical.php.
Its because of your theme your theme maybe have 404 page or function in functions.php you can remove it if you want check : http://codex.wordpress.org/Migrating_Plugins_and_Themes_to_2.3
