Half of kids aged 11 to 18 lie about their personal details on the web, says Kidscape.
Research by the charity, which has been conducted as part of Safer Internet Day, revealed of these, 60 percent lie about their age while 40 percent lie about their personal relationships.
Seven percent admitted they never tell their parents the truth when questioned about their online activities, while 83 percent claimed they had done something rude or inappropriate online, with boys twice as likely as girls to behave rudely or inappropriately on the web.
Furthermore, over 45 percent admitted they are sometimes happier online compared to their real lives, while 47 percent claimed they behaved differently online than in real life.
"We were alarmed by the number of risks being taken by teenagers while online. We know that safe online behaviour is taught in schools and by other organisations like us, but teenagers seem to be unable to relate the risks to themselves," said Peter Bradley, Kidscape's deputy director.
"These findings suggest that children see cyberspace as detachable from the real world and a place where they explore parts of their behaviour and personality that they possibly would not show in real life. We can't allow cyber-worlds to be happier places than our real communities - otherwise, we are creating a generation of young people not functioning adequately in our society."
Meanwhile, separate research by security firm Kaspersky revealed that 43 percent of web users have an online friend they've never met. Furthermore, a survey by EU Kids Online highlighted that 15 percent of 11 to 16 year olds had received sexual messages online, while five percent had been bullied on the web.
Kidscape hopes to reduce the number of children that have experienced cyberbullying through Share It - a campaign which encourage victims to share their experiences.
Kaspersky has launched a dedicated website that contains advice and guidance for parents, guardians and children about staying safe on the web.
"Protecting young people online means talking to them about the dangers and giving them the confidence and control they need to surf safely,” said Malcolm Tuck, managing director of Kaspersky Lab UK.
EU Kids Online also said 49 percent of parents whose kids surf the web from their mobile phone don't know what their children are looking at.