Don't use a dialog unless the user is leaving the page.
I might want to scroll while making an input decision. A dialog will interrupt me if I scroll the active row out of view, blocking my view of other items I'm comparing.
One of the advantages of tabular data is sorting and comparison. This allows you to sort your current rows, and make judgements across other items. This could be amounts due (in your case).
You might start editing, and realize that you should adjust your amount based on other items in the table. I would expect that I could scroll the list freely, and scroll back to my row I'm currently editing to input a final value.
I don't know how much sorting and comparison applies to this specific table, but it sets a pattern for other areas in your app to which this is helpful.
If users don't notice (test them first!), apply an indicator of status.
One alternative is to append a small label indicating the table has a row that may or may not be in view, but that's in an edit state. If you have a large amount of rows, you could even have a 'show' link that scrolls to the editable item.
My language probably isn't optimal (Maybe 'unsaved changes' is better), and I took some liberty by removing the visible 'Edit' buttons (could you maybe have the edit button only on hover for desktop views) to help focus on the edit state as you scroll the list.
If you need to enforce only one edit at a time
Again, my text is not optimal, but you could show a disabled Edit button, explaining to the user that simultaneous multiple edits are not allowed.