Abstract: The increasing utilization of fiber-reinforced thermoplastics (FRTPs) as a substitute for metal in load-bearing structures poses challenges related to NVH issues arising from frequency variations and reliability concerns stemming from fiber dispersion within the resin matrix. In this study, the steel automobile seat beam serves as a benchmark for comparison. FRTP beams are designed and fabricated using two distinct processes: compression molding and injection over-molding. Subsequently, their modal frequency and reliability are meticulously analyzed. Experimental investigations are conducted to explore the influence of various factors, including the combination of laminates and ribs, as well as the stacking sequence of laminates, on the modal frequency. The findings reveal that the modal frequency and vibration mode are subject to alterations based on the fiber type, beam material, and laminate stacking sequence. Notably, in comparison to the steel benchmark, the first-order frequency of the FRTP beam in this study experiences a 6.59% increase while simultaneously achieving a weight reduction of 32.42%. To assess reliability, a comprehensive analysis is performed, considering a six-fold standard deviation. This analysis yields the permissible range of fluctuation for material elastic constants, bending performance, and frequency response. Encouragingly, the FRTP beams meet the required reliability criteria. These results provide valuable insights for comprehending the stiffness-dependent response and effectively controlling structural performance when implementing FRTP for weight reduction purposes.