No. Without an internet connection, it won't be possible for someone to get into his computer. There is something called Van Eck Phreaking where if someone could get close enough to the computer monitor, they could see what's on the screen. This is very rare and Leo's never seen any real life demo of this.
There's another kind of phreaking that's more interesting that probably doesn't work with LCDs, but would work with CRT monitors. Even without seeing the screen, someone could stand outside of someone's window and use the flickering of the screen to see what's being displayed. This, Leo has seen demonstrated, but Terry would need some highly sophisticated people after him for this to be a concern. The NSA actually does have a standard for preventing this kind of espionage called Tempest.