Despite significant advantages, large-scale use of carbon-reinforced concrete has been hitherto limited due to insufficient thermal resistance and chemical compatibility with cementitious materials. In this regard, mineral-impregnated carbon fibers (MCFs) made with a geopolymer (GP) are a promising, novel reinforcement for GP concrete, making cement-free, lightweight, fireproof, and durable structures. This paper is envisaged to study the temperature-dependent pullout behavior of MCFs in GP concrete and for a comparison with a commercial, epoxy-impregnated product. The experimental results showed comparable load-transferring capacity and post-crack behavior at ambient temperature but better bonding quality at elevated temperatures for MCFs. These were explained by the material structures, failure patterns, and thermal behavior of the yarns and GP concrete, as characterized by micro-tomography, microscopy, thermogravimetric analysis, and mercury intrusion porosimetry. Finally, a three-dimensional, finite element model was used to simulate and predict the pull-out process through a combined discrete cohesive zone model and smeared phase-field method in a representative crack element framework. With proper parametric calibrations, evident agreement between numerical and experimental results was gained.