Hot air and steam heating are the most commonly used techniques for food powder pasteurization in the food industry. In conventional heating, heat is transferred from the hot air to the food surface and then it is transferred to the inside of the food matrix. Conventional heating is time and energy-consuming and the airflow may not be uniformly distributed in the powder. In this regard, radio frequency (RF) heating is a promising alternative technology for food powder pasteurization. The working principle of RF heating is similar to microwave heating but RF heating has a relatively deeper penetration depth in foods and lower equipment cost. Heat is generated by the interaction between RF energy and the molecules inside the food; thus, pasteurization is evolved from inside the products. Therefore, RF heating can greatly reduce heating time and save energy and cost as compared to hot air pasteurization. Despite the effectiveness of this method, heating uniformity is still a major concern of RF heating which is caused by the heterogeneity of food compositions and the non-uniform distribution of the electric field. In this study, to overcome the non-uniform heating limitation of the RF heating, the food powder container was surrounded by a liquid medium. First of all, the effect of container dimension and geometry on RF heating was evaluated to address the problem to be solved. Then, the effect of the surrounding medium on RF heating performance was investigated. As a final step, the proposed oil immersion system was validated via microbiological inoculation. RF heating of whole milk powder surrounded by soybean oil increased the heating rate by 25% compared to the one surrounded by air. E. faecium NRRL B-2354 was considered as a surrogate of Salmonella spp. for whole milk powder to validate RF pasteurization due to its higher thermal resistances than Salmonella spp. More than 5 log reduction of Salmonella spp. was achieved after RF heating the cold spot of the whole milk powder followed by holding it in the oven at 75 °C for 2 h.