It is very likely that there are such people. Proof for this is that Neville Longbottom was born to two Wizard parents, but his family thought he was non-magical when he was young.
From Harry Potter and the Philosopher's Stone chapter 7.
[…] ‘but the family thought I was all Muggle for ages. […] Great-uncle Algie came round for tea and he was hanging me out of an upstairs window by the ankles when my great-auntie Enid offered him a meringue and he accidentally let go. But I bounced – all the way down the garden and into the road. They were all really pleased. Gran was crying, she was so happy. And you should have seen their faces when I got in here – they thought I might not be magic enough to come, you see. Great-uncle Algie was so pleased he bought me my toad.’
Augusta Longbottom tells us that both of Neville's parents were magical in Order of the Phoenix chapter 23.
‘What's this?’ said Mrs Longbottom sharply. ‘Haven't you told your friends about your parents, Neville?’
[…] said Mrs Longbottom. ‘My son and his wife,’ she said, turning haughtily to Harry, Ron, Hermione and Ginny ‘were tortured into insanity by You-Know-Who's followers.’
‘They were Aurors, you know, and very well respected within the wizarding community,’ Mrs Longbottom went on. ‘Highly gifted, the pair of them. […]’
Neville's mother had come edging down the ward in her nightdress. She no longer had the plump, happy-looking face Harry had seen in Moody's old photograph of the original Order of the Phoenix. […]’
The photograph was described in more detail in chapter 9.
From an inner pocket of his robes Moody pulled a very tattered old wizarding photograph.
‘Original Order of the Phoenix,’ growled Moody. ‘Found it last night when I was looking for my spare Invisibility Cloak, seeing as Podomore hasn't had the manners to return my best one … thought people might like to see it.’
[…] ‘That's Frank and Alice Longbottom –’
Harry's stomach, already uncomfortable, clenched as he looked at Alice Longbottom; he knew her round, friendly face very well, even though he had never met her, because she was the image of her son, Neville.
‘– poor devils,’ growled Moody. ‘Better dead than what happened to them … […]’
Order of the Phoenix chapter 30 had also revealed that Frank Longbottom was an Auror, but didn't unambiguously claim that Alice was also a wizard.