how can i utilize a first person lock while also having a main menu screen?

in my game when a player spawns they are met with a main menu screen. in my game I would like to have a first person lock while also having the menu. how can I make it so the player's mouse is able to be used in the menu without being locked? in other words I only want the first person lock to occur once the person is outside of the menu... if that makes any sense...