Display Screen or Portion Thereof with an Animated Graphical User Interface

FIG. 1 is a front view of a display screen or portion thereof with an animated graphical user interface showing a first image thereof; and, FIG. 2 is a second image thereof. The outermost broken lines showing the display screen or portion thereof form no part of the claimed design. The remaining broken lines showing portions of the animated graphical user interface form no part of the claimed design. The appearance of an image sequentially transitions between the images shown in FIGS. 1 - 2 . The process or period in which an image transitions to another forms no part of the claimed design.