Many will say no and cite neuroscience as support, but imagine there was a person whose thoughts consisted only of an inner monologue saying "blah blah blah" over and over again. But at the same time the physical reactions taking place in their brain and body leads them to outwardly act like a completely normal person including reporting completely normal thoughts and feelings when asked about what they are thinking and feeling. How would we ever know what they were really thinking? Wouldn't we assume that their mental world is a normal one?
All neuroscience can show is correlations with behavior (and by behavior I am including when someone self-reports that they thought or felt something). That we see correlations with thought is based on faith, faith that our "theory of mind" capability is showing us the true reality of how other people really think rather than just a useful imagination of how other people think that works because we can anticipate each other's actions and behaviors and determine appropriate responses this way. We also tend to assume that if someone says they thought something or feel a certain way that that is that person's true mental reality but how do we know that's not just what physics is making them do whereas their actual mental reality is something completely different?
Thus thoughts exist on another level of reality in so far as they are truly unknowable. The only way for us to 'know' them is by faith, faith that when people speak about their mental experiences that this actually reflects those experiences and faith that the clues we see in each other's behaviors are giving us an accurate picture. Even in scientific studies they had to start the studies with something. Before scanning anyone's brain they had to use another method to determine what a subject was thinking or feeling, such as by asking them or observing facial expressions, or talking to a psychiatrist who observed the person. Yet these observations are truly just observations of behavior, so all we can know is that the brain correlations correlate with behaviors that human beings are accustomed to assuming (or carrying out actions (including speaking) that are labeled as meaning the person is "assuming") indicate certain mental phenomenon.