Don't worry the ghost in the Pokemon Tower in Lavender Town is part of the game in Pokémon Red, Blue, Yellow, Fire Red, and Leaf Green.
The ghost is actually the sprit of a deceased Marowak who died protecting it's child from Team Rocket.
In order to advance in the game you have to defeat the ghost but not before you identify it with Silph Scope.
If you don't have the Silph Scope, it can be obtained from the Rocket Hideout (which is underneath the Game Corner) after the player defeats Giovanni.
To find out more about the ghost Marowak click here.