Yes some counties of Arkansas allow you to assess your vehicle online but you would need to look up your counties assessing office online to find the correct place to assess your vehicle online.
Not all Arkansas counties allow you to assess your vehicle online but some do and if you can't assess your vehicle online you'll need to go to the county assessing office to have your vehicle assessed.
You need to assess your vehicle between January 1 and May 31 each year so make sure you get the vehicle assessed on time.