It's cloudflare's security measure and is intended to appear if your connection is suspicious for whatever reasons. Just type in the captcha and hope this stops happening or if it keeps being a nuisance, you might try contacting cloudflare's support.
The IP address you came from recently had bad activity online, so CloudFlare will present a challenge before you can access the website. Here's what you can do to solve the problem:
1. Passing the captcha will help reduce the threat score associated with the IP address. If no bad activity is seen from the IP address after a two-week period, then the challenge behavior will stop against that IP address.
2. You can also request that the particular site you're visiting whitelist your IP address when you pass the captcha and send a message to the site owner. If the site owner decides to whitelist your IP address, it does two things:
a) It allows you to access that site from that IP without further challenges for that site.
b) Helps correct false positives with IP data, which further helps reduce the threat score associated with the IP address.
Note: You must have cookies enabled to pass the captcha.