Traffic was backing up at the Calgrove entrance with at least one lane closed as a body covered by a white sheet sat on the right lane of the freeway.
The incident was reported to the California Highway Patrol around 5:09 p.m.
Investigators are looking into a report the man had exited a vehicle on the freeway for unknown reasons.
Shortly before 9 p.m., the lanes that were affected by the investigation were reopened.