As far as I know from my experience with Lync, the answer is no. In fact it would be irrational to do so. The list of frequent contacts exists to keep the information about people you have contacted frequently. Disabling this functionality defeats the purpose of having it.
I completely understand the reason why one would not want to see the list of frequent contacts. If you don't want to see it you can choose to hide it. People you contact will still be automatically added to the list, but it will not distract you any more.
In the "View More Layout Options" dropdown menu, unselect "Show Frequent Contacts"
After that you will only see your main contacts that you have added manually.
Good luck