Large, floor-to-ceiling windows were boarded up with plywood after being shattered at the Newport Harbor Republican Women on West Coast Highway, just west of Dover Drive.
The Republican Party of Orange County did not immediately respond to ABC7's request for comment.
Steel's office on Holder Street, between Cerritos and Katella avenues, was vandalized on July 26.
According to the congresswoman's staff, a rock was thrown through a second-story window.
"Violence of any kind has no place in our society," Steel said in a statement provided to ABC7. "I will not let this act of vandalism prevent me from providing a strong voice for my constituents in Washington. I am grateful that my staff were unharmed in this incident as local authorities continue to investigate."
No injuries were reported in either incident, and no suspects were in custody.