Namibia took to the crease first and it did not take long for the Australian strike bowlers to have their impact, with Josh Hazlewood taking the wickets of the openers.
All five Australian bowlers took at least one wicket, with leg-spinner Adam Zampa finishing with four for 12 off three overs, leaving Namibia all out for 72 runs.
David Warner and Travis Head built a partnership of 21 before Warner was caught off the bowling of David Wiese for 20 runs off eight deliveries.
Head top scored for Australia with 34 runs off 17 balls with Australia chasing the score down in the sixth over, with Mitch Marsh contributing 18 runs.
Australia sit at the top of Group B, while Namibia sit in third place with two losses and one win.