Khalida Jarrar was scheduled to be released on October 29. But her husband, Ghassan, said Thursday that her lawyer was informed of the extension.
Jarrar is being held under “administrative detention,” an Israeli policy that permits holding people for months at a time without charges.
In 2015, she served 15 months after being convicted of incitement to violence and “promoting terror activities.”
Jarrar, a senior member of the Popular Front for the Liberation of Palestine, was arrested again in July 2017 and has been in administrative detention since.
Her husband calls it a “political” detention.
The military had no immediate comment.