Do you have a long-term or permanent residence card?
And do you own a television?
If you answered yes to both questions, you have to pay a licence fee. No matter if you watch only internet TV or foreign channels or don’t watch the TV at all. Just the fact that you own a TV which can receive a TV signal is a ground for the licence fee.
And not only that. As your television can also (most probably) receive a radio signal, you should pay a Radio licence fee, too. You can expect a letter from Czech Radio to ask for that.
The point of both fees is to support the public and independent news service and broadcasting of Czech TV (Česká Televize, including local Brno News CTV) and Czech Radio (Český Rozhlas; including national broadcasting and news in English).
The TV fee is 135 CZK/month per household. The Radio fee 45 CZK/month per household.
The penalty for evading the obligation can be up to 10,000 CZK (according to the 348/2005 Bill).