Yes, as long as you meet criteria for filing. Pending I-751 is not a problem.
When you start N-400 online application, you are asked a few question to establish eligibility.
General N-400 requirements:
- You spent enough time in the US (physical presence) as LPR in the last 3 years (if want to apply based on marriage to US citizen) or in the last 5 years (if applying under general provision)
- If applying based on marriage, make sure you've been married to US citizen for 3 years and were LPR for 3 years.
- Make sure you never left the US for 6+ months on same trip, in the last 3 or years
- Make sure you always paid taxes and haven't had criminal charges in the last 3 or 5 years