Hi @Karthik,
This is very likely happening because the tickets on your board have been added to sprints from other boards. You can see the assignment of an issue to a sprint in the sprint field on each issue.
As soon as a sprint is present on an issue, that sprint is also displayed on the backlog view of any board the issue is on.
That basically means you should have a look of how you collaborate across different teams / boards and make solid working agreements on how you do sprint planning company wide.
Hope this helps!
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