The incident occurred Tuesday night when Maan Devi went outside her house to relieve herself. She lost her way in the darkness and reached a nearby colony, they said yesterday.
A girl sleeping outside her house got scared on seeing Devi, who was wearing a white saree, and raised alarm, the police said.
Soon locals gathered at the spot suspecting Devi was a witch and started beating her up, the police said, adding that by the time some women identified her, she was severely injured.
Her family members rushed her to an Agra hospital from where she was released after first-aid but she died on the way home.
Inspector D P Sharma of Doki police station said the woman was mentally-challenged. She received an injury on her head.
The body has been sent for postmortem, he said, adding a case of murder has been registered against two persons in the matter.
There has been increasing instances of women in at least five states who claim they found portions of their hair chopped off. Police are investigating the matter but haven't got any leads so far.