Seeing it on your PC
Printer software and network monitoring tools query devices on your network on 161.
Should you block it?
Fine on a local network. Nothing on a home PC should accept 161 from the internet, and old SNMP versions send their "community string" password in plain text.
Check it on your PC
Run this in PowerShell to see what is using port 161 right now, and which program owns it:
Get-NetUDPEndpoint -LocalPort 161 -ErrorAction SilentlyContinue | Select-Object LocalAddress,LocalPort,@{n='Process';e={(Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue).ProcessName}}No output means nothing is using the port at the moment. For every connection at once, paste netstat -ano into the netstat explainer.
Block it in Windows Firewall
In PowerShell run as administrator, this stops other computers from connecting to this port on your PC. It does not stop your own programs connecting out.
New-NetFirewallRule -DisplayName "Block inbound UDP 161,162" -Direction Inbound -Protocol UDP -LocalPort 161,162 -Action Block
Undo it with Remove-NetFirewallRule -DisplayName "Block inbound …", using the same name. If you depend on the service on your local network, this rule stops that too.