HuntinDog is correct... although your button's front shows the Great Seal of the United States, it is definitely a Fashion button, not a Military-issue one... because it has a self-shank back, which Military-issue ones never have.
For anybody here who doesn't already know:
The term "self-shank back" means the button's sheetmetal back has a couple of holes in it for the thread to pass through, instead of having a loop or other type of shank for the thread to pass through. The button's back itself forms the loop/shank, hence the term "self-shank back."
Secondly... your button's emblem shows remnants of red, white, and blue paint, which Military-issue Great Seal buttons never use.
Self-shank backs first show up in the very early 20th Century. A different version of self-shank back, having a raised rectangle with a tunnel through it, starts showing up in the mid-20th-Century. See the photos below. US Military-issue buttons never have these backs.