To investigate the rheological properties of basalt fiber asphalt mastic, a silane coupling agent was used as a modifier for basalt fibers, and the effects of varying fiber contents were analyzed. Cone penetration tests, bending beam rheological tests, and dynamic shear rheometer tests were conducted to evaluate the rheological properties of asphalt mastic consistency, high-temperature stability, and low-temperature cracking resistance under different temperatures and fiber contents. The findings show that the silane-coupled basalt fibers enhance the shear strength and consistency of asphalt mastic. After modification, the phase angle decreases; elastic response increases, and complex modulus improves. Adsorption capacity between fibers and asphalt increases significantly, enhancing high-temperature deformation resistance and low-temperature cracking resistance of asphalt. The optimal fiber content for silane-coupled basalt fibers is approximately 2.6%.