Sure.. Just locate your theme folder, will use 'Default' theme as an example, and open:
sp-resources > forum-themes > default > templates > spHead.php
You want to then find the function - sp_MemberButton, and comment it out. If you have a decent editor and haven't changed your template, you will find it on line 99. It should then look like:
/*sp_MemberButton('tagClass=spButton spRight', __sp('Members'), __sp('View the members list'));*/
I'd suggest commenting it out over removing it, this way you can enable it again if you ever decide you want to by removing the /* */
Two things however. Firstly this will not stop people from accessing the members list, they can still access the page via URL, there is just no button to it. You might want to consider the option of using permissions to stop people viewing the list, as there is a permission specifically for it under the 'Viewing' category.
And as always, we advise creating your own theme or making a child theme if you're making changes, as these changes could be lost in future updates.
Hope this helps!