Pretty much the title.
Thanks in advanced
When erasing on a Background rather than a regular layer, it’ll erase using whatever colour you have set as your background colour (which is black in your case). If you work on a regular layer, or select transparent as your background colour (right-click transparency in your palette), you’ll get the result you want.
How do you select a specific color as your background color?
Right click the colour in your palette, or Alt+right click from the artwork.