Yun is an IoT device which is intended to be used exactly for this reason -to access it from where ever you are-. The answer is simply yes, but not always. There are several things to keep in mind.Arduino Yun should be connected to Internet. Somehow it should be publicly available, which means configuring NAT, DDNS services, firewall, etc.Configuring them is not an overwhelming task, so do not be afraid to start. There are dozens of examples out there.