So if you are using full site of Facebook then go to setting >> security>>active session.
You will see here the place and device which used your account.if you don't recognize the place or device then you can disable it. You can see here the name of place and the name of device.if you have used only "Facebook for android" but u saw here "Nokia Lumia" or chrome etc,then click on the "end activity" just beside of the name of location and device.
If you are a mobile user then go to the account setting >> security >> active session and do the same as i told you above..tnq