When an officer places you under arrest, you usually are quite aware of the reason why. In most cases, even if you do not completely understand the reason, the officer has a legal right to place you under arrest.
In some situations, though, the officer may lack the legal authority, which results in a situation where the officer is breaking the law. According to Cornell Law School, false arrest is when someone of authority places you under arrest without the legal right to do so.
To arrest anyone, a person must have the right under the law to do so. Officer would need an arrest warrant or probable cause to place you under arrest. An officer cannot simply arrest you without any charge or reason for doing so.
Position of authority
To put you under false arrest, the person doing so must claim some authority to do so. For example, a law enforcement officer arresting you is doing so under the authority of his or her job, but another citizen arresting you would have no such authority. The officer could place you use false arrest, but the citizen could not unless that citizen stated that he or she had authority, even if the person is lying.
A false arrest does not require the arresting officer to have bad intent about the act. He or she may very well believe this is a valid situation. It could be a routine part of the job. It could be an honest mistake, but that does not make it legal.
If you feel your arrest was a false arrest, you have the right to question it in court, and you should do so.