Yes, it is. You can control it.
After creating dialog:
WindowManager.LayoutParams lp = dialog.getWindow().getAttributes();
lp.dimAmount = 0.0f; // Dim level. 0.0 - no dim, 1.0 - completely opaque
dialog.getWindow().setAttributes(lp);
Upd: you can even add blur behind the dialog:
dialog.getWindow().addFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND);
Upd2: Blurring is deprecated since API14:
This constant was deprecated in API level 14.
Blurring is no longer supported.
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