Exhibit 23(a) CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS As independent public accountants, we hereby consent to the incorporation by reference in this Post-Effective Amendment No. 1 to the Registration Statement on Form S-8 filed by MDU Resources Group, Inc. with the Securities and Exchange Commission (Registration No. 333-27877) of our report dated January 24, 2000 incorporated by reference into the MDU Resources Group, Inc. Annual Report on Form 10-K for the year ended December 31, 1999. /s/ ARTHUR ANDERSEN LLP Minneapolis, Minnesota March 23, 2000