PersonalIt is quite simple to keep any activities you do associated with Mendeley limited only to your followers in Mendeley.
In Mendeley Web, you can click the arrow next to your profile picture in the top right hand side of the screen, then select 'Privacy' (alternatively you can click here)
Here you can choose who to allow to see your profile page - everyone, or just the people who follow you on Mendeley.
Please be aware that any all actions in Public groups (either Public or Public: Invite Only) will be viewable by everyone. If you do not wish to have your actions seen in a group, you will need to create a private group.
Your library is restricted to you - only you can see the contents of your library, your folders, and your notes in All Documents.