Is it illegal to watch pornography on the computer?

If it's not kiddy porn, no.

Nope.

Hope not!

No, unless you're on a company or school computer, or watching kiddie porn.

If you're at home, on your own computer, you're good to go.

Generally no.

In some places yes.

Generally no. The internet is intended for freedom of expression. Sites that produce pornography are required under Federal Statute to advise that you have to be over 18 to view their site, but it's a self-checking system at best.

Looking at it on a work computer is probably not illegal, although likely to get you fired if caught. Same with schools.

If you work for the government, you are probably violating a law. Federal employees using gov computers are definitely violating a law, but each state may have it's own laws/rules when it comes to their employees.

Looking at porn in public places may get you busted on public indecency charges.

Probably not, but maybe . . . and it's complicated.

In the US, if you're an adult under the law of your state and you looked at Playboy mag online in your house, alone, you're probably safe (unless you're on a military base or within some other strange jurisdiction). If you're not an adult you may have a problem. If the material was more risqu茅 than Playboy, you'd have to consider whether the material was obscene. That determination can be hard (no pun intended), as it depends on where you live. So if you're looking at something pretty harsh, then you might have a problem by violating obscenity laws depending on where you live. And keep in mind that when you open a web page, technically you are importing pornographic material into whatever jurisdiction you are in. So you may run into trouble with laws against importing obscene material.
Realistically, unless you are viewing child pornography, using someone else's computer or network connection, allowing others to view it, or you're under age, no one will likely take the time to investigate your home computer use--even if you're looking at harsh materials.

watching pornographic materials is not illegal for consenting adults.
either on the internet or else.