Diagnosis
The temperature sensor is in the camera, and it's being fooled by its own heat or a draft. The camera's electronics generate a little warmth.
How to Fix It
First, check the camera's placement. Is it sitting directly on a warm baby appliance, in direct sunlight, or crammed in a corner with no air flow? Move it to a more open spot, at least a foot away from any heat source, and wait 30 minutes for the reading to stabilize.
If That Didn't Work
You can manually calibrate the temperature display. On the monitor, go to Menu > Temperature > Calibration. Use the arrows to adjust the offset up or down until it matches a known good thermometer in the same room. This doesn't fix the sensor, but it corrects the display.
Heads Up
The temperature reading is best used as a relative guide, not a laboratory-grade measurement. Watch for big swings rather than the exact number.