Seeing it on your PC
Normal on a work PC that talks to its domain controllers. Unusual at home.
Should you block it?
Never expose LDAP to the internet. On a home PC, outgoing LDAP to an internet address is unexpected.
Check it on your PC
Run this in PowerShell to see what is using port 389 right now, and which program owns it:
Get-NetTCPConnection -LocalPort 389 -ErrorAction SilentlyContinue | Select-Object LocalAddress,LocalPort,RemoteAddress,RemotePort,State,@{n='Process';e={(Get-Process -Id $_.OwningProcess -ErrorAction SilentlyContinue).ProcessName}}Get-NetUDPEndpoint -LocalPort 389 -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 TCP 389,636" -Direction Inbound -Protocol TCP -LocalPort 389,636 -Action Block
New-NetFirewallRule -DisplayName "Block inbound UDP 389,636" -Direction Inbound -Protocol UDP -LocalPort 389,636 -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.