The Meghalaya police said the woman's five children, locked up in the house along with their father by the assailants, first saw them assault their mother and then blow her head off. The men fired six rounds directly at the woman's head, the police said.
The attackers allegedly belong to the Garo National Liberation Front.
The Meghalaya police said the incident occurred in a remote village of the district. The woman was about 35 years old.
There has been outrage in the country and globally after two young girls were gang-raped and found hanging from a tree in Uttar Pradesh last week.
In a statement yesterday the US said it is "horrified" at reports of sexual violence and murders in India. "Like so many in India, we were horrified to learn of these violent sexual assaults and murders. Our thoughts are with the victims' families during this difficult time," State Department Deputy Spokesperson Marie Harf said.