Authorities are not releasing details about the threat and haven't revealed if there have been any arrests.
Newark Mayor Ras Baraka said Newark police were notified about the threat by the United States Capitol Police.
Members of the department's Executive Protection Unit were assigned to Booker's residence in Newark.
Booker, a former Newark mayor, recently traveled to Alabama to campaign for Doug Jones, who won the state's special Senate election over Roy Moore.
----------
* More New Jersey news
* Send us a news tip
* Download the abc7NY app for breaking news alerts