Yes, it is likely an HF antenna for ham radio. If you did not connect it to anything, then it is just a resonant wire. There is probably no reason to disturb it since it is totally passive and is not really doing much up there. It would not be amplifying or affecting your radio/TV reception any more than passive electrical wiring or coax cables for your TV or internet affects reception. If you wish to tell us the dimensions/geometry of the wire we can probably tell you what band(s) it was being used for.
View a collection of "stealth" HF (high frequency, i.e. 3.5 MHz to 28 MHz, 80 meters to 10 meters) attic antennas here→
https://duckduckgo.com/?q=HF+antenna+in+attic
Some hams are restricted in what they can put up outside, or they don't have big trees, or don't want to put up a tower, so they will construct their HF antenna in the attic. Another stealth antenna is to wrap a wire around the entire house under the eaves. But the "tail" end has to be connected to a radio receiver, for the wrapped wire to do anything useful.