Analysis of magnetotelluric (MT) data in the northern Appalachian region reveals various heterogeneities in lithospheric structure. By inverting a subset of the long-period Earthscope USArray MT data, we obtained a 3D electrical resistivity model that provides insights into the previously identified seismic low-velocity Northern Appalachian Anomaly (NAA). We compared the resistivity (inverse of conductivity) values with empirical conductivity models based on an olivine-orthopyroxene-clinopyroxene mantle mineral assemblage. Low-resistivity anomalies in the inverted model suggest an anomalously hot mantle in the northern and western edges of the NAA. Both in the north and west, resistivities in the uppermost mantle are sufficiently low to require a small fraction of partial melt. Additionally, we resolved a resistive feature in western New England that extends deep into the mantle lithosphere and is absent in seismic velocity models. We interpret this feature as dry and depleted lithospheric mantle. The observed heterogeneities in the lithosphere may reflect ongoing asthenospheric upwelling caused by combined effects of weakened lithosphere from past hotspot interactions and present edge-driven mantle convection.