It would be not serious -- maybe "light-hearted" is a better word than "humorous."
It doesn't have to mean, "I heard the order and I will carry it out." It is a general acknowledgment: "Okay, I got it."
The person on the other end may be sending data or information rather than instructions -- or even just a greeting.
"Hello, Richard. Beautiful day today, isn't it!"
"Roger. I'll see you at lunchtime."
"Roger that!" often means "Yes, I agree! You're correct!"