"The woman is in critical condition after she was stabbed three times with a sickle," he said.
He said the attackers were armed with traditional weapons such as sickles, arrows and other crude weapons.
Bagus said the attackers also stole 60 bullets.
The OPM, comprising a small group of separatist rebels, have been fighting a sporadic rebellion in Papua, formerly Irian Jaya, since the early 1960s.
Papua, a predominantly ethnic Melanesian province 3,700 kilometres north-east of Jakarta, is a former Dutch colony that became an Indonesian province in 1964.