They were chatting huh. Maybe your mum only saw the popup on
screen and din notice where your hand was? Well, at least you were
not totally exposed, dude.
Anyway, I believe your dad will understand lar. And you're almost
an adult already, right? 
Most parents will respect their children's privacy more when they
become adults.
RELAX, don't worry about it. Your parents may approach you to talk
about it, or they may not.
If they talk to you about it, tell them the truth. Say that you
were surfing "those sites." Being mature about it is usually the
best thing to do in this situation. I should know, I've had one of
these "talks" with my dad before.
When i was around 14, one day, a bunch of friends came over to my
place, and one of them brought a cd with .jpg pics of nude girls.
We printed out some of the pics, then suay suay one printout
somehow ended up under my bed. I dinno about it until my dad found
it a few days later. Kaoz, I was quite embarrassed. When he asked
me about it, I was too stunned to say anything but the truth.
Guess what, he said he was glad that i was truthful, and frank.
Then he said he understands that young chaps are naturally curious
about the female body, and that IT WAS BETTER THAT WE KNEW
SOMETHING ABOUT IT, rather than be totally blur.
Then he told me about the dangers of casual sex, that sex outside
of marriage should be avoided, etc. Basically, we just had a chat
lar.
It was awkward, but im glad we got through it. All dads want to
make sure that their children don't end up sexually wayward, you
know what I mean. Sleep around, etc. But it's just damn awkward to
initiate. This could be an opportunity for the both of you to get
it out of the way, let your dad get it out of his system.
Relax, there's nothing to worry about. If it comes, then be mature
about it. It might actually be better if yall sit down to talk
about it, since your mum might have seen the porno stuff on screen.
Just let your parents know that you are not doing anything sexually
deviant.
Calm their fears, k. Don't worry about it. 
