A mobile wireless communications device may include a portable housing, a substrate carried by the portable housing, and wireless communications circuitry carried by the substrate. The mobile wireless communications device may also include at least one an antenna assembly carried by the substrate and coupled to the wireless communications circuitry. The at least one antenna assembly may include an electrically conductive base conductor having a first rectangular base portion and a second rectangular base portion offset therefrom. The first and second base portions may be coupled at respective diagonally opposing corners thereof and having an antenna feed defined along an outer portion of one of the first and second rectangular base portions. The at least one antenna assembly may include at least one electrically conductive arm extending along at least one side of one of the first and second rectangular base portions and spaced apart therefrom.