If I am not connected to the router but I know the router IP address is it possible to access the router page by entering the router ip in the browser?
No, you need to connect to the network to be able to access the router's settings. The router is on it's own LAN network (usually at 192.168.0.1 or 192.168.1.1 etc) which other devices get onto when they connect. You'll need to connect to it to get onto the same network as the router, by ethernet or WiFi, to be able to access the router and it's settings - going to 192.168.1.1 on another network won't be going to the same device as 192.168.1.1 on your routers network.
Think of it like having a door number of someones house - you need to be on their street to meet them at their door. You can't find the same person with the same door number on a different street - networking works in the same way.
You have not mentioned Internet connection at all, but if that's what you do mean, then the router doesn't need to be connected to the Internet for you to connect to the router and then access it's settings - internet connection is completely separate from your LAN access to the router and other devices in your LAN.
You said “IF I am not connected ..”
I think most people would know that your router must be connected to something, normally a network or a computer.
That said, you can access your router by IP address.
I do this very frequently.
http://192.168.x.y normally works. You might need https://
But whichever form, it always works for me. Windows or Linux, any modern browser.
The router does not need to be connected to the Internet.
But I assume your router is connected to the computer (or the other way around).
This is a very confused question.
Where are you in relation to the router? By "IP" do you mean the router's LAN or WAN address? Are you wanting to use WiFi to do this?
Most routers reject admin requests from the WAN address & are frequently set to reject from WiFi addresses.
In short, many are set to only allow admin requests whilst directly connected to the internal LAN.