This is one of the most frequently reported recurring anxiety dreams, and its meaning is fairly consistent: keys represent access — to a place, opportunity, or relationship — and losing them reflects a worry about losing that access.
Searching frantically for lost keys
The classic version, this usually appears during ordinary periods of mild overwhelm, similar to the "can't find your car" dream — many small responsibilities competing for attention rather than one major crisis.
Keys that don't fit the lock anymore
Can reflect a sense that access you used to have — to a relationship, role, or opportunity — no longer works the way it used to, even if you're not sure why.
Someone else having your keys
Often points to a feeling that control over your own access to something important currently rests with someone else — worth identifying who, and to what.