Yes, you can use an extension cord for a TV. However, it's critical to double-check that the cord is qualified for the power you require.  Most TVs require at least a 10-amp circuit. So, you'll need an extension cord that can handle that much power.  Besides, it's always a good idea to have a few extra feet of cord so you can move the TV around if necessary. It's always good to have too much cord than not enough.