If you're talking about one account logged in from one IP address, logging out, then logging back in later on a different computer, sure that's fine.
If you're talking about multi-logging, or playing more than one account at the same time, this is allowed, as long as doing so does not provide an unfair advantage, such as rigging minigames(not that anyone plays minigames anymore). Multi-logged accounts are allowed to interact with one another - however, if one account is determined to have violated the game rules and involves another account(for example, using one account to bot resources and sell them, then trade the gold to another account), Jagex can trace the trades and ban all accounts involved.Aslon Dak: Still 'Scaping after 15 years!
It's fine even if the different computer is say a few hours away from your normal computer?
Yes, that should all be fine. I've done this myself with no issues.
Be safe. Avoid public Wi-Fi. Also, be certain that you're the only one with access to your account. Don't share your account with anyone else. If you get someone else interested in RS, great! Encourage them to make their own account, so you can play together. Anyone with your login info can easily change your password, locking you out of your account. Your character and everything they own would become the other person's account faster than you can say "I got hacked, and I helped them do it!"
Finally, any website page, YouTube video, or other source that is not part of Jagex's official RS site that asks you to enter your login and password is trying to scam you. Never trust your information to these risky third-party sites.
Happy 'Scaping! Aslon Dak: Still 'Scaping after 15 years!