I was checking my activity monitor for Safari, and I see this number as its average energy usage. Is it normal?
It is not normal according to the "Avg Energy Impact" column. It is awkward to have more than 10,000 value for the "Avg Energy Impact" column, especially from Safari. Please contact Apple Support if you see this consistently.
You should consider the "Energy Impact" column as it shows the real-time energy usage.
The "Avg Energy Impact" column shows the average energy impact for the past 8 hours or since the Mac started up, whichever is shorter.
For more info : Apple Documentation - Activity Monitor