Maybe. Try the first option below, then the next if that doesn't work, and so on:
If you are still in your image editor:
Hit Command-Z (Mac) or Ctrl-Z (Windows) to undo your LAST change. (This will only work if you did not save the change you want to undo.)
If your image editor has a "Revert to Saved" option, use it to get your image back to the state it was in immediately before you saved it. (This will only work if you did not save the changes you want to undo.)
If you're in Photoshop 5 or higher, use your "History" palette to go back to the pre-saved image.