You can lock your Node Editor view so that any new nodes you create do not appear in the graph.
Click this icon 
to unlock your view. The Node Editor view is locked by default.
Note: You can still perform delete and undo in locked mode.
Tip: You can also lock the view by disabling the Options > Add to Graph on Create option under the Node Editor Options menu or from the Node Editor work area marking menu. See Node Editor Options menu and Node Editor marking menus for more information.