It is possible the circuit is overloaded, but only at certain times, like when the refrigerator compressor turns on while other things are also on. That may only happen at certain times a year.

What else is on that circuit?

thanks. there are couple of outlets on the kitchen counter and the small microwave oven above our oven. The last time it tripped, I was standing in the kitchen, and I saw that there were no other gadgets that were active, nor was the microwave. I am wondering if there was some loose connection or frayed wiring that might be causing intermittend arcing somewhere in the circuit. Could arcing cause the breaker to trip? thank you

yes, arcing is a short and would make the breaker trip. But try replacing the breaker first. Arcing would not normally come and go (unless there is a problem in the refrig). Breaders go bad and act weird sometimes.