The men, who have been named as suspects, are thought to have been planning to attack the local parliament in Pekanbaru, the capital of Riau province, national police spokesman Setyo Wasisto said in a statement.
During Saturday’s raid on a faculty at Riau University, police found a pipe bomb, a homemade grenade, as well as the homemade explosive triacetone triperoxide (TATP), known as the “mother of Satan”, Wasisto said.
They also seized an air rifle and sets of bows and arrows, as well as other material such as fertilizer that could be used to make bombs, he said.
Authorities have highlighted concerns about a rise in radicalism at universities in the world’s biggest Muslim-majority country.
A number of recent surveys of students have pointed to significant support for Islamic State, carrying out jihad and the establishment of a caliphate in Indonesia.
After some major successes tackling Islamist militancy in the last two decades, there have also been a resurgence of attacks in recent years.
Last month, police shot dead four men who used samurai swords to attack officers at police headquarters in Pekanbaru.
That attack came soon after a series of suicide bombings by militants targeting churches and a police building in Indonesia’s second-biggest of city of Surabaya.
In all, about 30 people were killed in the attacks in Surabaya, including 13 of the suspected suicide bombers.
Police say the bombers belonged to cells of the Islamic State-inspired Jemaah Ansharut Daulah (JAD), an umbrella organization on a U.S. State Department terrorist list that is reckoned to have drawn hundreds of Indonesian sympathisers.
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