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Subsurface imaging is key to understanding the origin of intraplate volcanoes. The Changbaishan volcano, located about 2,000 km away from the western Pacific subduction zone, has several debated origins. To investigate this, we compared regional seismic tomography with the electrical resistivity results and obtained high‐resolution 1D and quasi‐2D velocity‐depth profiles. We show that the upper mantle is characterized by two anomalies exhibiting distinct features which cannot be explained by the same mechanism. We document a localized low‐velocity anomaly atop the 410‐km discontinuity, where the P‐wave velocity is reduced more than that of the S‐wave (i.e., lower Vp/Vs). We propose that this anomaly is caused by the reduction of the effective moduli during the phase transformation of olivine. The other anomaly, located between 300 and 370 km depth, reveals a significant reduction of the S‐wave velocity (i.e., higher Vp/Vs), associated with a reduction of the electrical resistivity, altogether consistent with partial melting. Plain Language Summary: On Earth, most magmatic activities occur at plate boundaries, which can be explained by plate tectonics. However, the largest intraplate volcanic region in northeast Asia, the Changbaishan volcano, is situated on the border between North Korea and China about 2,000 km from the plate boundary and has several debated origins. We show that beneath the Changbaishan volcano, the upper mantle is characterized by two seismic velocity anomalies exhibiting distinct features which cannot be explained by the same mechanism. The shallower anomaly located between 300 and 370 km depth is interpreted to be due to a small amount of melt because of its seismic and electrical resistivity characteristics. The other deeper anomaly atop the mantle transition zone at ∼ 410 km depth cannot be explained by partial melting alone and is likely caused by a change in seismic characteristics as a result of the olivine phase transition that occurs at that depth. Key Points: The upper mantle beneath the Changbaishan volcano is characterized by two seismic low‐velocity anomaliesThe shallow low‐velocity anomaly (i.e., shallow than 370 km, with a higher Vp/Vs ratio) is due to partial meltingThe deep anomaly (i.e., atop the 410‐km, with a lower Vp/Vs ratio) is likely caused by the moduli reduction during the phase transformation [ABSTRACT FROM AUTHOR]