Hi @sanatandebnath
A yellow light on the Ethernet port indicates that data is being sent/received between the laptop and the network that it is connected to.
If the green light is on, it means that the laptop is connected to the network but no data is being sent or received by the laptop.
If you're not doing anything online the computer may be doing things online in the background e.g. checking for updates etc.
It could also be that the laptop has a virus or malware is installed, so perhaps running a full anti virus, anti malware check would be worth considering