A police spokesman said they had received the information during the night and investigated it Sunday morning.
"Reliable state security sources" informed the police that "a concrete danger existed from an attack with an Islamist background," the spokesman said.
The carnival, known as the "Schoduvel," is the largest in northern Germany and was expected to draw a crowd of 250,000 to Braunschweig, also known in English as Brunswick, with 4,500 participants in the procession and some 100 floats this year.
Immediately before the carnival was cancelled, the German interior ministry had reacted to Saturday's terrorist attack in Copenhagen by saying their was no elevated risk of an attack in Germany.
As always, there was an abstract level of danger, a ministry spokeswoman in Berlin told dpa. "But we do not have any concrete indications of attack plans in Germany," she stressed. "The situation is unchanged."
She added that German security authorities were in contact with their Danish counterparts, but as investigations in Copenhagen were ongoing, it was too early to draw any conclusions as regards Germany.
Two people were killed and five injured in the Copenhagen attack before police shot dead the suspected attacker on Sunday morning.