Close active Facebook sessions using a computer:
Log in to your Facebook account and click down arrow located on the right-hand side of the blue bar that’s near the top of the Facebook window.
Click Settings.
Click the Security and Login link on the left side of the screen.
Scroll down to the section labeled “Where You’re Logged In” and click the See more link.
You should now see a list of all the devices that are currently logged into your Facebook account.
The first device in the list should be the device you’re using right now. Any other devices that are listed are also logged in to your account. I recommend that you log those devices out remotely by clicking the three vertical dots over on the right and then clicking Log Out.
Close active Facebook sessions using a mobile device:
Log in to your Facebook account and tap the Menu button (it looks like three horizontal lines).
Scroll down and tap the Settings & Privacy link.
Tap the Settings link.
Tap Security and login.
Scroll down to the “Where you’re logged in” section and tap the See all link. You should now see a list of all the devices that are currently logged into your Facebook account.
Tap on every device that shouldn’t be logged into your account (that would typically be every device that you aren’t using right now) and then tap Log Out.