Is it normal to be interested in other people while in a relationship?
Yes. Being in a relationship doesn’t switch off your ability to notice or feel drawn to other people; what matters is how you handle it and what boundaries you and your partner have agreed on.
You can love your partner and still find someone else attractive, enjoy a bit of attention, or get a passing crush. Lots of people do. A feeling isn’t the same as a decision to pursue it, and it doesn’t automatically mean there’s something wrong with your relationship.
People differ on what they’re comfortable with, though. Some are fine with harmless flirting; others see it as crossing a line. If this interest is becoming secretive, taking up a lot of energy, or pushing against your agreements, it may be worth talking with your partner about boundaries—and what you might be looking for.