The attack, which left two people seriously injured, occurred around 8.00 pm (18:00 GMT) late Thursday night before just a few minutes before a curfew imposed by authorities as part of COVID-19 lockdown period.
Eyewitnesses reported seeing a man showing an object, believed to be a stick-grenade, through the window of the packed hairdressing salon that then exploded.
The man was then killed by a explosive device, an eyewitness told APA in Kigali.
In a statement earlier, police said that the attacker entered the salon and proceeded to occupy the seat from where he was to get a haircut, but then told his barber that he had something in his pocket which he tried to show the barber.
In the meanwhile, Rwanda National Police (RNP) confirmed Friday that seven out of the 11 people who were injured by a grenade explosive were discharged from hospital.
The suspect is described as a 25 year-old man who is a resident in nearby area.