Oman were bowled out for 133 with Khurrum Nawaz top scoring on 23 and Scotland's Safyaan Sharif taking 3-33.
The Scots reached their target with an over to spare, thanks to Matt Cross (47) and Calum MacLeod (35 not out).
Earlier, Kevin O'Brien's 40 helped Ireland beat United Arab Emirates by 24 runs to secure a last-four place.
Scotland had already been sure of their place in the semi-finals after beating Hong Kong and the Netherlands in Group B.
All three remaining games also take place in Dubai on Friday, with Group A winners Afghanistan and Oman contesting the first semi-final before Scotland and Ireland meet, and then the final.
Scotland beat Oman by seven wickets in Dubai to finish top of their Desert T20 Challenge group and will face Ireland in Friday's second semi-final.