emailEditText.setError("Invalid Email");
emailEditText.setError(null);//removes error
Custom Icon
Drawable drawable = getDrawable(R.drawable.ic_error_outline_black_24dp);
drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
users.setError("error", drawable);
References
http://stacktips.com/tutorials/android/edittext-validation-in-android-example
https://stackoverflow.com/questions/13195852/how-can-i-remove-edittext-error-and-request-focus-in-android