Synergy often occurs between coal and biomass during co-utilization, and the combustion reactivity and combustion properties of coal are affected mainly due to high volatile matter in biomass. However, it is not clear that a synergistic interaction will be encountered if coal is processed with biochar that contains a limited amount of volatiles due to charring process. In this article, the existence of synergy was questioned based on the thermal analysis data obtained from the co-combustion of several biochars and lignite. The biochars produced at 400 °C from lignocellulosic biomasses such as Fraxinus (FR—ash tree), Populus hybrids (PO—hybrid poplar), and Rhododendron (RH) were blended with Turkish lignite (Adıyaman-Golbasi) to form blends that contain 5–15% biochars. These blends were burned in a thermogravimetric analyzer, and the combustion characteristics of the blends were evaluated, considering the criteria that include the reactivity and combustion performance indices including ignition index, comprehensive combustion index, burnout performance index, combustion stability indices, and rate and intensity index. Also, synergy indices such as synergy indicator, synergy factor, and interaction coefficient were calculated to identify the presence and intensity of synergy. It was concluded that depending on the type of biochar and the addition rate, changes occurred in the combustion properties of the coal, which can sometimes be considered as additive behavior and sometimes as a synergistic interaction. The presence of 5% or 10% PO biochar in the blends resulted in very obvious synergies in combustion characteristics according to all eight criteria considered.