You should use finish()
when the user clicks on the button in order to go to the previous activity.
Button backButton = (Button)this.findViewById(R.id.back);
backButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
finish();
}
});
Alternatively, if you really need to, you can try to trigger your own back key press:
this.dispatchKeyEvent(new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_BACK));
this.dispatchKeyEvent(new KeyEvent(KeyEvent.ACTION_UP, KeyEvent.KEYCODE_BACK));
Execute both of these.