The limitations of raw materials in the production of Portland cement concrete for construction processes, the emission of greenhouse gases due to production and the high cost of using alternative materials and products have turned it into an attractive challenge for engineers and researchers. Therefore, geopolymer concrete containing fibers as an environmentally friendly mixture and a structure by replacing aluminosilicate pozzolans instead of cement has been a significant effort to replace Portland cement concrete. In this research, a stable mixture with structural characteristics containing polypropylene fibers has been designed and produced. The mixtures developed with changes in the size of polypropylene fibers in three lengths of 6, 12 and 18 in different percentage ratios of alkaline solution to pozzolan were produced and subjected to mechanical and thermal evaluation. The use of fibers with a length of 12 mm has the most optimal size in terms of resistance in the construction of geopolymer concrete, and the compressive strength of this sample is 4.9 and 19.7 percent, respectively, compared to the samples made with 6- and 18-mm fibers. The age has increased by 28 days. It shows an increase in the ratio of alkaline solution to pozzolan from 0.4 to 0.425 for geopolymer samples. Also, in samples with solution to pozzolan ratio equal to 0.4, the highest drop at 700 degrees Celsius was related to samples containing 18 mm fibers and then 12 mm, and GC samples with fibers containing 6 mm has less drop. In addition, the mixing designs obtained along with the mechanical properties under elevated temperature at the age of 28 days were modeled using artificial neural network and multiple linear regression models. The model based on artificial neural network has shown an acceptable performance in predicting the mechanical properties of ternary blend fiber reinforced geopolymer concrete.