The Wisconsin Department of Natural Resources is investigating the attack, which happened near the town of Comstock in Barron County.
The 69-year-old victim reported the attack around 2 p.m. Saturday, the DNR said.
She was able to call 911 and was taken to a local hospital for treatment, but her condition is unknown.
Officials who responded to the 911 call found a cub in a tree, indicating that the incident involved a female bear and a cub.
Authorities tried to track the bear with the help of a trained bear hound dog, but the search was unsuccessful, the DNR said.
The DNR said efforts to capture the bear are ongoing. Several bear traps have been set at the scene. The goal is to euthanize the bear and assess its condition.
Why the bear attacked was not immediately clear.