The motive for Wednesday's attack was not immediately clear, but Indonesia, the world’s most populous Muslim-majority country, has suffered a resurgence in homegrown militancy in recent years, with some attacks targeting police.
National police spokesman Dedi Prasetyo said the perpetrator had died and four officers and two civilians, one of whom was a police employee, had been wounded by the blast in a car park at Medan police headquarters at 8:40 a.m.(0140 GMT).
"All pieces found at the scene will be tested by a forensic lab to determine the type of bomb," Prasetyo told a news conference.
Indonesia's anti-terrorism unit, Densus 88, was investigating whether it was a "lone wolf" attack or linked to a radical group like the Islamic State-inspired Jamaah Ansharut Daulah (JAD), which has carried out a series of attacks in the country, he said.
Television broadcast images showed smoke and a shower of fragments coming from the parking lot area and people rushing out of buildings around the headquarters after the blast.
The suspected attacker, who was wearing a jacket and a backpack, had his bag checked before entering the car park near an area where people were queuing for clearance letters, said North Sumatra police spokesman Tatan Dirsan Atmaja.
The attack comes a month after a suspected Islamist stabbed and wounded Wiranto, Indonesia's former security minister, after he had opened a university building in Pandeglang, west of Jakarta. Wiranto, who like many Indonesians uses just one name, has since been discharged from hospital after undergoing surgery.
The government scrambled to tighten its anti-terrorism laws after a series of suicide bombings linked to the JAD group killed more than 30 people in the city of Surabaya last year.
Foreseeing an increased threat of attacks from Indonesians who joined Islamic State and have begun returning from the Middle East, police have detained hundreds of suspects since the start of the year.
Police spokesman Prasetyo said a man arrested on Tuesday in Bekasi, near Jakarta. He said the man was believed to have fought in Syria and was a suspected JAD member, though he did not draw a direct link to the attack in Medan.Stanislaus Riyanta, a terrorism expert, said the attack in Medan could be in retaliation for the death of Islamic State leader Abu Bakr al-Baghdadi, who killed himself last month during a U.S. commando raid on his compound in Syria.