This is incorrect. Currency issued by a central bank is not a real liability, since its issuance does not entail a future payment obligation. It's a liability only for accounting purposes. The government bonds on a central bank's balance sheet are used to conduct (or the result of) open market operations. They aren't "backing" anything.
In USA, Treasury issues currency and coin. Private organization named Federal Reserve has special privilege to manipulate interest rates through various means.
