Monday's and Tuesday's threats caused class disruptions on campuses across the country.
FOX 5's Maureen Umeh says law enforcement agencies, including the ATF and FBI, are investigating are investigating the incidents.
Officials at Howard university in the District say they received a second threat from an unidentified caller on their university phone line just before 3 a.m. Tuesday involving "multiple areas" of its campus.
The school was put on lockdown for over two hours, and after a search, an all-clear was given when no threats were found.
Since the all clear, both campus and D.C. police, have increased their presence on campus, Umeh says.
Other area HBCUs, like Bowie State University, Morgan State University and UDC also received threats.
Since Monday, more than a dozen historically Black colleges and universities have reported bomb threats. Law enforcement officials are working to see if the incidents are connected.