Yes. When using data networks (cellular data or WLAN) to access for example Internet, your phone uses an IP address, either a dynamic IP address (default) received from the network or a static IP address specified in the phone.
At this time, there is no way to assign a static IP address to your Windows Phone Wi-Fi. As a possible workaround, you will find out the MAC address of your Windows Phone device and then set up a DHCP reservation at a particular IP for that MAC address. You can access your MAC address by going into Settings > About > More Info and see you MAC address listed.