I am using a Uniden Bearcat BC345CRS scanner and it has a antenna connector. I need to know which type of antenna connector is that and what kind of connector can be used to connect any other external antenna to it?
Yes, definitely. BNC is a common connector for scanner antennas, the other variation you'll run into is called SMA, which will look like a tiny threaded stud similar to type-f (like something that would connect to coax TV cable connection but smaller)
Also there are tons of adapters available to use other connections to your BNC connector.