If you have implemented a logon and are tracking who logs in and out you could certainly run a query against the log table for log on with out log off.
Determining if they are active or not in the db would be a horse of a different color.

I have not setup the logon, however the users computer Id is recorded when they are using access in the Log In Log out table. I am looking for something like how on this site it shows user is online and its highlighted.

I don't know what your knowledge level is outside of the couple of Beginner courses I see that you have here.  

I'm sure it could be accomplished but I think it would take a bit of programming to accomplish.
Sorry, I don't have a great answer for you.  I have not tried this before and, to the best of my knowledge, nothing like this has been covered in any of Richards videos.

Just as an aside, I might have my browser open and show that I'm online but in truth it is minimized a good portion of the day and isn't really a good indicator if I'm actively engaging in the forum.  A similar scenario would be the case with you database.  Tracking actual activity or interaction with your database would be a different much more difficult thing to do - In my mind anyway.

Maybe one of the other guys or Richard will have additional input for you.

Yea, you would first need to know who is logged in, then you would need to create something to track keypress or other events happening inside of the forms that would keep the most recent action time and keep replacing the value as they interact with the database. Then you could use a timer event to see who has a "recent action" within the last 15 minutes or whatever and mark them as online.