With such a broad definition as events or things not associated with scientific knowledge, paranormal activity could refer to almost anything. What I think of when I hear paranormal activity first and foremost is aliens and/or UFO's.
Many claim to have seen some type of Alien life, whether it be that of a UFO or weird happenings affecting their use of technology. Though a person who experienced the phenomena directly is convinced that they saw a craft or being from another galaxy, there are logical explanations to what they may have seen. However, when alien activity occurs it almost always is accompanied by flashing lights, erratic movement and, as if to seal the deal, no sound whatsoever. In other alien findings, some are able to communicate with these unknown creatures, but have never been able to catch it on film, or record what they're experiencing. I for one am not convinced. I personally, have no belief in aliens or UFO's. There is constantly so much going on in the sky that we have little knowledge about, so I feel like it is unfair to make assumptions that aliens are making visits to earth and messing with us.