The man has admitted the offence, according to KTH’s head of security, Lena Edvardsson.
The 33-year-old had threatened to shoot students attending the university.
“We are going to have police officers in attendance at the institute to inform people about the situation,” Edvardsson told news agency TT.
The security chief confirmed that the university will remain open as normal.
In making the threats on an internet forum, the anonymous person stated that they would take a gun to the institute on Monday and shoot as many people as possible.
Both KTH and the police took the threat seriously and worked intensively to find the source of the threat and avert it.
Ulf Göranzon at Stockholm police confirmed that the man has admitted to putting the threat on the internet.
“At 12.30pm we traced the suspect. We followed the electronic trail he left on the internet,” Göranzon said.
A warrant was soon after issued for the man’s arrest and he was detained during the night in Gothenburg. The man was interviewed first at around 4am. According to media reports he is a student at Chalmers University of Technology in Gothenburg.
The police hope to gain more detailed information over the incident from subsequent interviews.
“The first interview has consisted of a lot of formalities. We have informed him of the suspicions. More thorough interviews will take place when a defence counsel has been appointed,” Göranzon told news agency TT.
The man, who is suspected of unlawful threats, remains in Gothenburg but Göranzon presumes that he will be transferred to Stockholm.
Fifty police officers have been deployed at KTH on Monday and Göranzon confirmed that some will remain despite the arrest of the suspect.
“We will have a police presence at KTH, but we will adapt the force according to needs,” he said.