The militants lobbed the grenade at Cherapur Moirang Palli Bazar in Thoubal district at around 8 PM yesterday.
A woman vendor identified as Sanahanbi (55) fainted after hearing the deafening sound of the grenade.
She was taken to Thoubal district hospital where her condition was stated to be out of danger, the sources said.
No individual or group has claimed responsibility for the incident.