Guwahati's Senior Superintendent of Police A.P. Tiwari said seven people sustained injuries in the blast that occurred close to the railway station in an area that is usually crowded.
Tiwari said the blast took place around 7.55 p.m.
The high security Paltan Bazar police station in the city, a popular market place, is also close to the Guwahati Railway Station, which normally remains crowded. However, the area was not as crowded at the time of the blast as it was a Sunday.
"According to witnesses, two youths came on a motorcycle and lobbed a grenade. However, we can confirm this only after a detailed investigation," the police said.
No one has yet claimed responsibility for the explosion.
Assam Chief Minister Tarun Gogoi had recently stated that ULFA militants were trying to carry out subversive activities in the run-up to Independence Day, Aug 15.
The chief minister cancelled his official visit to South Africa, scheduled earlier this week, after violent incidents elsewhere in the state.
On Tuesday and Wednesday last, militants had triggered three blasts in Lakhimpur and Karbi Anglong districts of the state, killing one person and injuring several others.
The spurt in violence is attributed to the anti-talk faction of the United Liberation Front of Assam (ULFA), and the Assam Police has subsequently sounded an alert across the state.
Police had earlier received information that militants would be targeting police and security forces in the run-up to Independence Day.