If you are like most users of AutoCAD and do not create 3D content, you probably do not use the ViewCube in the top-right portion of the drawing window.
If this is the case, you can turn off the ViewCube through OPTIONS.
1. Go to OPTIONS - command line type 'OP'
2. Select the 3D Modeling tab
3. Remove the check mark for "2D Wireframe visual style"