OMAC can refer to:
- OMAC (Buddy Blank), a DC Comics superhero
- OMAC (comics): an organization of powerful cyborgs that exist in the DC Universe
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- The OMAC Project, a limited series dealing with the OMACs
- Michael Costner, the last OMAC cyborg standing, chronicled in the OMAC (2006) miniseries
- Old Man's Aircraft Company, a business aircraft company which made several prototypes of the Laser 300 plane in the late 1980s and early 1990s
- One-key MAC, a construction in cryptography
- Order of Malta Ambulance Corps, an Irish first-aid organisation linked to the Sovereign Military Order of Malta
- OMAC (Industry Organization): Organization for Machine Automation and Control