This research aims to investigate the effect of using different weight percentages of metakaolin and mica powder on the mechanical properties and durability of the samples. Studying the effect of using steel fibers with a volume percentage of 1% on the mechanical properties, especially the bending and tensile properties of geopolymer mortar, is one of the goals of this research. In total, 20 samples of different mixing plans were made from geopolymer mortar, containing metakaolin, mica, Ground granulated blast-furnace slag, and steel fibers. Metakaolin and mica were replaced by slag with weight percentages of 5%, 10%, and 15%. The tests performed in this research include compressive strength (at ages 7, 28, and 90 days), bending strength at the age of 28 days, direct tensile strength at the age of 28 days, compressive strength after exposure to temperatures of 100°C, 200°C, 400°C, and 600°C, Flexural strength coefficients of heated and unheated samples, initial and final water absorption tests, electrical resistance tests, and scanning electron microscope tests. The results of the compressive strength test showed that the concentration of sodium hydroxide solution had a significant effect on the outcomes of the aforementioned tests. Additionally, the results indicate the positive effect of mica on improving thermal resistance under high temperatures (600°C). In both groups A (without fibers) and B (containing fibers) with sodium hydroxide concentrations of 4 and 8 M, the replacement of 5% mica increased the bending strength by 14.7% and 3.3%, respectively, compared to the control sample. An increase in the percentage of mica replacement resulted in a decrease in the flexural strength of geopolymer mortar.