Resting HR increased during the day - is this normal?

I've noticed a behaviour that seems a little bit strange to me:

Usually when I wake up I step on the scale and sync my Enduro with Garmin Connect, taking note of the resting heart rate that, I assume, is calculated based on my heart rate during sleep.

However on several occasions I've noticed that when I sync the watch with Garmin Connect in the evening the resting heart rate has increased - usually by 2 or 3 bpm, but on one occasion it has increased by almost 10 bpm. I've noticed that this happens on my rest days only when I do little to no physical activity (working from home, sitting all the day in front of my computer).

Is this the expected behaviour?