If you're choking on your Saliva frequently then it means that something is not right so you should see your doctor to find out what exactly is causing the Choking on the Saliva.
However the most common reason people frequently choke on their Saliva is because the muscles that are involved in swallowing weaken or stop functioning properly due to other health problems.
Either way it's not normal to be choking on the Saliva and a doctor can find and likely rectify the problem.