Hi Viruses should not be treated by antibiotics, but there are some antiviral treatments that might be used. Many diseases are viral like mumps, measles, flu, colds through to rabies, Ebola, lassa fever, SARS just to mention a few.
Sally has named some Viral infections that you can get and they definitely shouldn’t be used with antibiotics! Antibiotics are to be used for bacterial infections only and viruses should be treated by antivirals. If you were infected by both a virus and a bacterium though it would be OK to use antibiotics then. For example people with HIV tend to also get tuberculosis and so they need both antivirals and antibiotics.
Wikipedia lists the most common viral diseases. Some you will recognise (influenza – also known as ‘flu), some you won’t (rotavirus – causes the condition known as “stomach flu” though it has no relation to influenza).
Occasionally, viruses can make the patient very very ill and they may require treatment other than simple antivirals. One of the things occasionally required in very ill patients is antibiotics to invent any additional bacterial infections whilst the immune system is in a weak state trying to fight the virus.