It depends. Is this your router within your premises? Does the message appear frequently?
If yes and given your router is handing out IP addresses using DHCP its probably just a router error / mishap.
Assuming your router is using WPA2 encryption you should be safe - a perpetrator that already was able to crack your encryption should have no issues getting an IP address anyway.
In summary (assuming its your router):
- make sure it is configured to use WPA 2 encryption. Make sure your WPA 2 password is rather lengthy, uses random characters, numbers an special characters like slashes, backslashes, stars, etc.
- maybe you ask a friend who is somewhat literate with computer stuff if you do not feel fit to do that yourself
- don't worry too much. As said probably just a networking glitch
- please answer the questions already given in the previous post (as well as the questions above). Without knowing your environment and where this is happening all we can give is some general hints and guesswork.