Maybe. But probably not. More likely it means someone is forging sender addresses on your server to send spam (most likely not your server, though it could be) and misconfigured mailer daemons all over the world are sending the undeliverable spams back to you. And of course you can't do anything with them; they end up frozen in your queue.
How to solve it? There's no easy way to learn how email works. You need to figure out who's sending the mail back to you and why. The only way to do that is to study the emails in the queue. It may be time consuming, and it's probably not something you'd want to outsource to a company charging by the hour, so you might want to just roll up your sleeves and learn .
Somebody is probably spoofing an email address on your server, using an email address hosted on your server as the return email address in their spam. When its rejected, it returns most of the times as < > on a bounce.