Nabi hit an unbeaten 84 off 54 balls under pressure to guide Afghanistan to 164-6 before Mujeeb claimed a career-best 4-15.
"We have so many good players at the moment and we just need guys to jump out the box and be a lot more consistent."
Najibullah Zadran hit a blistering half-century as Afghanistan beat Zimbabwe by 28 runs in their first match of the tri-nation T20I tournament.
Afif, batting at number eight, hit eight fours and a six in his maiden international fifty that guided Bangladesh to 148-7 in 17.4 overs.
Tamim Iqbal continues to miss out after requesting a break from international cricket.
"It is important that we support our captain, whether it is Masakadza or anyone else, by creating an environment in which we can be confident."
He will now return to the cricket action in November when Bangladesh is expected to tour India to play two Tests and three T20Is.
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