Facebook thinks it knows your political preferences based on your activity! This includes pages you like, political articles you like, etc. They use this information to target you for politically-charged ads.
See what Facebook has you labeled as by doing the following:
-> Settings & Privacy
–> Account Settings
—-> Your information
—–> Review & Manage Your categories
——> US politics
You can be labeled as: (1) very liberal, (2) liberal, (3) moderate, (4) conservative, or (5) very conservative.