In general: if it is a lan, then it's a private address not routed in the internet, therefore almost safe. Just your router gets a wan ip from your provider, which is never private. Your router change the 192.168.x.y address with the wan ip - even when you have 10 Pc's in your private network, nobody outside your lan can see it, because your complete lan looks from wan side like one device with one ip address and this is your router. What does it mean? Well, when somebody is trying to hack you, he is always trying to hack the router (your wan ip), but never one of your pc's. Only packets from inside (your pc's) can leave your lan through wan by changing the ip-address and only requested content (websites) will be received from your router and after changing the wan to lan ip forwarded to your pc.
But you should read something to understand, why you need a firewall aso.