No, generally. Unlike securities like stocks, treasuries are not listed in a formal exchange like the New York Stock Exchange. As an alternative, you can purchase a treasury bond between the counterparties over the counter.
This entails contacting a broker or bank by phone or stopping by an Electronic Commerce Network (ECN) during an auction. They are therefore accessible to all investors, and you can invest directly in treasury bills without using a middleman.
US Treasury bonds have a low default risk since the federal government guarantees them, despite the fact that they trade over-the-counter.