Dallas police have given the all clear, hours after security levels were raised at their headquarters in the city.
They said they had received an anonymous threat, two days after the killing of five police officers.
A nearby parking lot was searched for a "suspicious person" but no-one was found. SWAT officers were earlier deployed at the main building.
On Thursday, five white police officers were shot dead by a black man, Micah Johnson, during a protest rally.
The march was against the killing of black men by police. Two deaths this week have led to nationwide protests.
Dallas police said its officers - using dogs - searched the parking lot but the hunt turned up nothing.
In a statement earlier on Saturday, the police said: "The Dallas Police Department received an anonymous threat against law enforcement across the city and has taken precautionary measures to heighten security."