An AA poll of more than 19,700 drivers indicated that a quarter (25%) feel car drivers and cyclists are behaving worse than before the outbreak.
This is compared with 21% who think cars are being driven better, and 10% who believe cycling has improved.
AA president Edmund King said: "Less traffic doesn't mean that drivers should start drag-racing at traffic lights, dangerously overtaking others or ignoring the speed limits.
"Drivers should also leave a wide 'social distance' when overtaking cyclists.
"Equally, this isn't a time for cyclists to pretend they're in the Tour de France and ignore mini-roundabouts and stop signs."
Many police forces have reported an increase in speeding during the coronavirus lockdown, as some drivers turn quieter roads into racetracks.
The Metropolitan Police enforced 800 speeding offences last week, more than triple the total during the same period in 2019.
This included one driver caught doing 93mph in a 30mph zone, and 34 incidents of drivers exceeding 100mph.
The AA survey indicated that pedestrians appear to be the lockdown stars, as 25% of drivers think walkers are behaving better than before the pandemic.
Mr King went on: "It's good to see that pedestrians on the roads are perhaps being more vigilant than before.
"As we approach the summer, it's likely that more people will be heading to the great outdoors for their daily exercise so we've all got to be a bit more considerate.
"If we all have patience with others, slow down and keep our distance, especially around those on family bike rides and walkers with young children, everyone can enjoy their time outside in peace."