| Onar Onarheim | |
| Office: | Minister of Fisheries |
| Term Start: | 28 August 1963 |
| Term End: | 25 September 1963 |
| Primeminister: | John Lyng |
| Predecessor: | Nils Lysø |
| Successor: | Magnus Andersen |
| Office2: | Member of the Norwegian Parliament |
| Term Start2: | 1 October 1961 |
| Term End2: | 30 September 1969 |
| Constituency2: | Hordaland |
| Birth Name: | Onar Selmer Onarheim |
| Birth Date: | 15 October 1910 |
| Birth Place: | Kvinnherad, Hordaland, Norway |
| Death Place: | Stord, Hordaland, Norway |
| Party: | Conservative |
| Spouse: | Borghild Lauritzdatter Aas |
| Children: | 2 |
Onar Selmer Onarheim (15 October 1910 - 2 April 1988) was a Norwegian politician for the Conservative Party. He was born in Kvinnherad.
Onarheim served in the position of deputy representative to the Norwegian Parliament from Hordaland, during the terms 1961 - 1965 and 1965 - 1969. From August to September 1963, he served as the Minister of Fisheries during the short-lived centre-right cabinet Lyng.
Onarheim was a member of Stord municipality council from 1947 to 1964 and 1979 to 1983, serving as mayor since 1954 and deputy mayor in 1982 - 1983.
Onar Onarheim had two adopted children, Onar Onarheim Jr. and Torunn Onarheim Staurset.