This study sought the predictive powers of motivation and self-efficacy on physics learners’ achievement within the theoretical framework of Skinner Theory of Operant Conditioning. Correlational research design was adopted for the study with a population of 6,205 SSII Physics students in public schools in Benue State and a sample of 375 SSII learners. Learners’ Psychosocial Factors scales and Physics Academic Achievement Proforma were used for data collection. The internal consistency reliability indices of 0.78 and 0.81 using Cronbach alpha method for the two clusters of the Learners’ Psychosocial Factors scales.  Data were analysed using regression analysis. Results showed that motivation and self-efficacy had 51% and 63% predictive powers on learners’ academic achievement in physics respectively. One of the implications of the findings is that low motivation and self-efficacy of learners will result to low achievement in physics. It was recommended that favourable academic environment should be provided for the learners to promote their motivation and self-efficacy.