The findings followed disclosures by arrested Jamat-ul-Mujahideen Bangladesh (JMB) terrorist Habibur Rahman Sheikh.
A senior NIA official said: "We have recovered five fabricated hand grenades, a timer device, three electric circuits, suspected explosive substance, different components for making IEDs or rockets and several other incriminating materials from Bengaluru on July 7.
"These hand grenades were fabricated as part of a conspiracy to commit terrorist acts in different parts of the country."
The NIA arrested Habibur Rehman Sheikh from Dodabalpur in the Karnataka capital on June 25. It recovered two IEDs from a drain in Ramanagara in Bengaluru a day later.
According to the NIA official, the accused also revealed his involvement in several instances of robberies committed in Bengaluru in 2018 in order to raise funds for JMB's activities.
Sheikh was a close associate of senior JMB leader Jahidul Islam alias Kausar and was associated with other JMB leaders such as Rahamatullah Sheikh and Moulana Yusuf.
He was named in a chargesheet filed by the NIA in March 2015 for his involvement in a conspiracy to wage war against the governments of India and Bangladesh.
The Bangladesh government banned the JMB in 2005 and India in May this year.
On Tuesday, the JMB operative was produced before the NIA Special Judge in Bengaluru which granted five days' transit remand for producing him before the Special NIA Court in Kolkata.
( With inputs from IANS )