Hey, if I use "Mobile Tethering" and share a network with my computer, will the network admin be able to see my activity on my computer?
Yes, Its possible to do so. Here, I am adding a link that can guide you to the process. I am sure that will help you out in the pursuit of getting your query answered without any bias.
https://www.quora.com/How-can-I-check-what-people-are-surfing-using-my-WiFi